5. Peterson, J. C, J. N. Socalis, and D. J. Durkin. 1980. Promotion of
leaf abscission in intact Ficus benjamina by exposure to water stress. J.
Amer. Soc. Hort. Sci. 105:788-793.
6. Poole, R. T. and C. A. Conover. 1983. Influence of simulated shipping
environments on foliage plant quality. HortScience 18:191-193.
7. Risse, L. A., W. G. Kindya, T. Moffitt, W. R. Miller, and R. E.
McDonald. 1980. In-transit temperatures of leatherleaf fern and cel
ery
shipped
in commercial and experimental
van containers to
Europe. U.S. Dept. Agr. AAT-S-11.
8. Risse, L. A., W. R. Miller, and T. Moffitt. 1982. Shipping fresh fruits
and vegetables in mixed loads to the Caribbean. U.S. Dept. Agr. AATS-28.
9. Sterling, E. P. and W. H. Molenaar. 1985. Transport tolerantie van
potplanten. Sprenger Institute Vol. No. 39. The Netherlands.
Proc. Fla. State Hort. Soc. 99:234-237. 1986.
COMPARISON OF STEM STRUCTURE IN FLORIDA GROWN PEPEROMIA
Margaret J. Mustard
Department of Biology
University of Miami Coral Gables, FL 33124
Additional index words. Piperaceae, anomalous stem, secret
ory structures, trichomes.
Abstract. A comparison of the stem structure of 10 species and
two varieties of Florida grown Peperomia shows that all are
anomalous. A continuous cylinder of collenchyma occupies
from 19 to 49 percent of the total stem area. The balance of
the stem is composed of a central core of parenchyma contain
ing scattered vascular bundles. The average number of vascu
lar bundles range from 10 to 40 in the species investigated.
All species were found to contain secretory structures within
the collenchyma and glandular trichomes in the epidermis.
The scattered distribution of vascular bundles resembles the
arrangement commonly found in monocotyledons rather than
dicotyledons.
The genus Peperomia includes several hundred species
distributed in the tropical and subtropical regions of the
world. Due to the attractive foliage, Peperomia are popular
as ground covers, in planters and in hanging baskets. The
cultivars are numerous and their taxonomy confusing. The
designation of species and varieties used by Florida nurse
rymen has been followed in this study.
Numerous workers have described the anomalous stem
structure of Peperomia (1, 2, 3, 4). The occurance of scat
tered vascular bundles in the stems of Peperomia resembles
those common in monocotyledons rather than in dicotyle
dons. This investigation was undertaken to compare the
stem structure of some Florida grown Peperomia with those
reported in the literature.
Materials and Methods
Twelve Florida grown Peperomia representing ten
species and two varieties of these species were selected for
investigation. Samples taken from the third internode of
each specimen were fixed in FAA, evacuated, dehydrated
and embedded in paraffin-plastic.
Contribution No. 257 from the Program in Tropical Biology, Ecology
and Behavior of the Department of Biology, University of Miami. The
author acknowledges indebtedness to Gann's Tropical Greenery for the
plants used in this research.
234
Results and Discussion
Transverse sections show considerable variation in
shape ranging from nearly cylindrical, to undulating, to
angular in outline (Fig. 1-12). The average stem diameter
at the third internode ranged from approximately 2 mm
in P. fosteri to 7.4 mm in P. magnoliaefolia 'Black' (Table 1).
The epidermis of all species is uniseriate and covered by a
cuticle of varying thickness. With the exception of P. fosteri
and P. puteolata both of which have thick cuticles, the re
maining species have relatively thin cuticles. The thickness
of the cuticle may be associated with the relative humidity
and water availability in the native habitates of the differ
ent species.
Glandular trichomes were observed in the epidermis of
all twelve specimens. On the more cylindrical stems, these
were distributed at random, whereas, in undulating stems
they were more frequently observed within the recessed
areas of the stem (Fig. 17). Glandular trichomes observed
on these specimens appear to be synonymous with the
hydathodes described by Yuncker and Gray (4) as occur
ring in the epidermis of the stems of Hawaiian Peperomia
and by Johnson (2) in Jamaican grown specimens. Since
the term, "hydathode", is usually associated with the pro
cess of guttaton from leaves, the designation of glandular
trichome seems preferable.
In addition to glandular trichomes, unicellular
trichomes were observed on P. fosteri, P. obtusifolia and P.
griseo-argentea 'Nigra' (Fig. 18). P. blanda showed a profu
sion of multicellular trichomes in the epidermis (Fig. 19).
It is possible that other specimens also have either unicellu
lar or multicellular trichomes which were absent from the
areas where the sections for this study were made. The
multicellular trichomes are similar in structure to those
described by Yuncker and Gray (4) for Hawaiian Peperomia
and by Johnson (2) in P. hispidula from Jamaica.
Directly internal to the epidermis is a continuous ring
of collenchyma (Fig. 1-12) which occupies from 19 to 49
percent of the total stem area in the different species
(Table 1).
A central core of parenchyma (Fig. 1-12) constitutes
from 51 to 81 percent of the total stem area in the different
species (Table 1). Within the parenchyma are located
numerous scattered vascular bundles (Fig. 1-12). The
number of vascular bundles varies from 10 in P. glabella to
40 in P. magnoliaefolia 'Black' (Table 1). Numerous investi
gations have been made pertaining to the distribution of
the vascular bundles in various species of Peperomia and
are summarized by Metcalfe and Clark (3). Briefly these
include specimens in which the vascular bundles are deProc. Fla. State Hort. Soc. 99: 1986.
Fig. 1-12. 1. Transverse sections of stems. 1. P. glabella x 45. 2. P. fosteri x 45. 3. P. obtusifolia x 40. 4. P. magnoliaefolia x 40. 5. P. amplexicaulis x
40. 6. P. scandens 'Variegata' x 45. 7. P. magnoliaefolia (variation) x 40. 8. P. viridis x 40. 9. P. magnoliaefolia 'Black' x 40. 10. P. blanda x 45. 11. P.
griseo-argenlea 'Nigra' x 40. 12. P. puteolata x 45.
Proc. Fla. State Hort. Soc. 99: 1986.
235
Fig. 13-19. 13. Transverse section showing secretory structure in the collenchyma. Note remnants of the lateral walls, x 125. 14. Tangential section
showing secretory structure in collenchyma. Note breakdown of both transverse and lateral walls, x 250. 15. Transverse section showing secretory
structure in which one large cell is surrounded by a sheath of smaller cells, upper one shows breakdown of lateral wall of large central cell, x 125.
16. TangentiaJ section showing large central cells surrounded by a sheath of smaller cells, lower one shows breakdown of lateral wall, x 125. 17.
Glandular trichome x 250. 18. Unicellular trichome x 400. 19. Multicellular trichome x 125. SS, secretory structure; GT, glandular trichome; UT,
unicellular trichome; MT, multicellular trichome; unlabeled arrows point to ruptured cell walls.
236
Proc. Fla. State Hort. Soc. 99: 1986.
Table 1. Anatomical features of Florida grown Peperomia.
Average
stem
HiampfPT*
Average % stem area
consisting of
Average
number of
collenchyma parenchyma
bumdles
vocri i lor*
Species
(mm)
P. glabella
P.fosteri
P. obtusifolia
P. magnoliaefolia
P. amplexicaulis
P. scandens
'Variegata'
P. magnoliaefolia
(variation)
P. viridis
P. magnoliaefolia
'Black'
P. blanda
P. griseo-argentea
'Nigra'
P. puteolata
5.1
37
63
10
1.9
49
51
34
4.5
37
63
28
6.3
24
24
4.5
23
76
77
2.7
24
76
15
6.1
24
76
26
4.1
19
81
22
7.4
22
28
78
72
40
32
38
68
22
18
2.6
5.9
2.6
62
28
22
scribed as scattered and those in which the outer bundles
are arranged in one or more irregular rings surrounding
a central core of scattered bundles. Due to the difficulty of
delineating between irregular rings surrounding scattered
bundles and simply scattered bundles, the Florida grown
species are all described as having scattered vascular bun
dles.
Secretory structures were observed within the collen
chyma and to a lesser extent within the parenchyma of all
species. In transverse sections, these structures appear to
consist of two types, one in which remnants of the vertical
walls are clearly evident (Fig. 13) and the other in which
one large central cell is surrounded by a sheath of smaller
cells (Fig. 15). In longitudinal sections, both types were
found to consist of articulated, anastomosing cells (Fig. 14
and 16). All specimens were found to contain the first type
while P. obtusifolia, P. magnoliaefolia, P. amplexicaulis, P. vir
idis and P. blanda were also found to contain the second
type. Yuncker and Gray (4) report the occurrence of
"mucilage canals" within the parenchyma of stems of P.
oahuensis. Until the chemical identity of their content has
been adequately determined, it seems advisable to desig
nate these as secretory structures rather than mucilaginous
ducts or laticifers.
Conclusion
Although this investigation shows that variations in
stem structure in Florida grown Peperomia exists, the un
derlying similarities of the anomalous stems prevail. The
stems of all varieties are covered by a uniserate epidermis,
all have a continuous ring of collenchyma and a central
core of parenchyma in which numerous scattered vascular
bundles are located, all contain secretory structures and all
have glandular trichomes. Their differences lie primarily
in the precentage of the stem area occupied by collen
chyma versus parenchyma and the number of scattered
vascular bundles present in the different species.
Literature Cited
1. DeBary, A. 1884. Comparative anatomy of the vegetative organs of
the phanerogams and ferns. Charendon Press, Oxford.
2. Johnson, Duncan S. 1914. Studies in the development of the
Piperaceae. II. The structure and seed-development of Peperomia hispidula. Amer. J. Bot. 1:323-328.
3. Metcalfe, C. R. and L. Clark. 1950. Anatomy of the dicotyledons.
Charendon Press, Oxford.
4. Yuncker, T. G. and W. D. Gray. 1934. Anatomy of Hawaiian
Peperomias. Bernice P. Bishop Museum. Occasional Paper 10:3-19.
Proc. Fla. State Hort. Soc. 99:237-239. 1986.
INFLUENCE OF RHIZOME HARVEST DATE, LENGTH OF STORAGE
AND GA3 ON SPROUTING AND FLOWERING OF ACHIMENES
B. K. Harbaugh and J. P. Gilreath
IFAS, University of Florida
Gulf Coast Research £sf Education Center
5007-60th Street East
Bradenton, FL 34203
Additional index words. Achimenes grandiflora.
Abstract. Studies were initiated to determine if cultural prac
tices could be developed to enable production of flowering
Achimenes grandiflora Dc. from stored rhizomes for spring
holiday sales, such as Mother's Day. In one series of tests,
rhizomes were harvested 19 Aug., 15 Sept. or 21 Oct., 1983;
stored at 20°C; and planted 18 Jan., 1 Feb., or 15 Feb., 1984.
Days to sprouting and flowering increased as dates of harvest
were delayed, and decreased as length of storage increased
for rhizomes harvested in August and September. In another
Florida Agricultural Experiment Stations Journal Series No. 7739.
Proc. Fla. State Hort. Soc. 99: 1986.
test, rhizomes harvested 15 Sept. or 21 Oct. were soaked 8
hours in a 0, 50, 100, 200, 400, or 800 ppm GA3 solution 24
hours before planting on 1 Feb. As GA3 rate increased, days
to flowering decreased when rhizomes were dug 21 Oct. Days
to flowering was unaffected by GA3 when rhizomes were dug
15 Sept., and days to sprouting was unaffected regardless of
harvest date. These data and additional trials in 1984-85
and 1985-86 indicated that by harvesting achimenes
rhizomes from mid-September to October and planting from
mid-January to February (depending on the date of Mother's
Day), flowering plants sould be scheduled for Mother's Day
sales.
Achimenes have typically been grown in Florida for
summer sales. Rhizomes used for their production are gen
erally planted from mid-January through April in order
to have flowering plants from late May through August.
Although achimenes make ideal flowering plants for Flor
ida's hot summers, this production schedule does notcoin237