ECOLOGY OF ASCLEPIAD LIANES 
103 
fig, JO. Transverse sections of lower stems from approximately 18 week-old plants of Marsdenia australis (A) 
and \Rhyncharrherta linearis ( B), showing thick-walled epidermis (E) and hypodermis (H), trichome (T; cut short 
in sectioning), cortical chlorenchyma (Co), a druse (D), external phloem (EP) and phloem fibres (F), secondary 
xytem with vessels (V) and thickened rays (R). internal phloem (IP) and pith (P) with lysigenous cavities 
(arrowed). Scale bars = 0.1 mm. 
The fast germination found here is similar to 
that found for a range of dry-country succulent 
asclepiads (Harp 1987). 
SEEDLING GROWTH 
Seedlings 5 to 15 days old were planted one per 
pot into 80 x 150 mm pots containing two parts 
sandy loam, one part vermiculite and one part 
perlite with controlled release fertilizer (‘Nutri- 
cote’,Chisso Asahi Co. Ltd, Tokyo, Japan) at the 
recommended rate. There were 10 replicates x 2 
species x 2 treatments (16/14°C and 25/15°C). 
Otherwise growth cabinet conditions were as for 
the germination trials except for a 14 hr photo- 
period. The seedlings were moved into the cabi¬ 
nets after four weeks at 25/15°C. None was given 
a support to climb on. All plants were dry- 
weighed at 105°C at an age of 18 wk. 
Results and discussion 
For all plants of both species introduced to 
16/14°C, shoot growth rapidly slowed and then 
stopped. By contrast, 25/15°C produced rapid 
growth, with shoot length more than twice as 
long in Rhyncharrhena but shoot dry weight very 
similar in both species (Table 2). At 18 weeks, 
the Marsdenia seedlings at 25/15°C already had 
a well-developed tuberous root system while 
Rhyncharrhena had much thinner, non-tuber- 
ous roots. This difference correlated with much 
higher Marsdenia root dry weight which in turn 
resulted in higher total dry weight for that 
species (Table 2). While Marsdenia root weight 
increased 6.5 times from 16/14°C to 25/15°C, 
Rhyncharrhena increased less than twice. At 
16/14°C the tubers of Marsdenia were very 
poorly developed. How this relates to climate 
and drought survival in the field requires further 
work. 
% I I. A. scanning electron micrograph of a Rhyncharrhena linearis node, showing stem (S), petiole (P), axillary 
Du a (A) and foliar gland (G). Scale = 0.03 mm. B, head of gland showing pore (arrowed). Scale = 0.3 mm. 
