LANKESTERIANA


FIGURE 5. Stages during in vitro development of P pearcei, P. longifolium and P humboldtii cultured on MS 50%.


the protocorms of P. pearcei and P. longifolium began
to develop the first leaf. On the other hand, the first
leaf of P. humboldtii appeared in the eighth week of
culture. The seedlings of P. pearcei and P. longifolium
developed two or more leaves within the first three
months, and began to develop roots in 3.5 months
(Fig. 5). The plantlets of P. humboldtii developed
their leaves in three months too, but began to develop
roots only after five months in culture (Fig 5). Higher
growth rate and better leaf development was observed
with Knudson C (data not shown).
 All plants were successfully acclimatized after
ca. 15 months of culture in vitro (Fig. 5). After six
months in the greenhouse, each plant of P. pearcei
had 7.32.5 roots, with the longest one measuring
10.41.7 cm in length. At the same moment, the
plants ofP. longifolium had 3.60.9 roots, the longest
one with 11.73.5 cm.

 Discussion

 The time it takes an orchid capsule to reach full-
maturity varies according to genus and species. Times
registered in this work for P. pearcei, P. longifolium
and P. humboldtii (10, 16 and 32 weeks, respectively)

LANKESTERIANA8(2), August 2008. O Unversidad de Costa Rica, 2008.


were considerably shorter than those measured in
other species belonging to the Cypripedioideae
subfamily. For example, Paphiopedilum callosum
capsules required between 47 and 48 weeks to open
(Arditti 1992). Moreover, it is not unusual to observe
differences in this respect between species belonging
to the same genus. For example, while capsules of
Laelia gouldiana needed 17 weeks to open, those
of L. purpurata required 31 weeks. Similarly, in
Dendrobium kingianum the time until full ripeness
was 20 weeks, while in D. nobile it was 41 weeks
(Arditti 1992).
 Capsule development in the three Phragmipedium
species studied characterized by an initial growing
period of around eight weeks, followed by a
maturation period in which the fruit did not increase
in size until opening (Fig. 1). This growing pattern is
commonly observed in many fruits. It is characterized
by a sigmoid arrangement, in which cell division and
elongation initially occur, followed by growth halt
and finally the fruit reaches maturity (Agusti 2000).
Those phases could vary in duration, depending on
the species or genotype, as it was observed in the
three Phragmipedium species studied here.