IN ANGIOSPERMAE. ROOT-CLIMBERS 159 



40 cm. with small segments 2-5-4 cm. long, similar to what we find in the 

 leaf of Rhaphidophora. 



G. The form of leaf is that of the plant that is ready to flower ; 

 another form has yet however to appear. 



H. Long pendent stolons often arise which possess broad oblong or 

 almost round leaves, cordate at their base and nearly sessile. 



If the Pothos-form grows upon a rock or a wall the higher development 

 does not take place 1 , but on a tree-stem it can and usually does develop 

 into the Rhaphidophora-form when it has grown higher. Cuttings of the 

 Rhaphidophora-form never revert to the Pothos-form, but both forms 

 develop into the long pendent stolons with round widely-separated leaves 

 when they grow out beyond their support. According to Ridley the 

 development of the Rhaphidophora-form has nothing to do with light as 

 it frequently appears in dark parts of the forest, whilst the Pothos-form 

 does not develop further upon a rock or a tree-stem exposed to the light ; 

 but perhaps there are wanting here the other factors necessary to normal 

 growth, such as moisture, and the juvenile condition of the plant is 

 therefore retained as happens in the Coniferae referred to above. It would 

 be of great interest were this examined experimentally. The allied 

 species Anadendrum marginatum and Anadendrum montanum have no 

 juvenile form of this kind. 



Some climbing plants belonging to other families behave like these 

 aroids, and the resemblance with Marcgravia is so complete that their 

 juvenile forms have been often confounded in gardens 2 . The species of 

 Marcgravia are amongst the most striking climbing plants of the tropical 

 American flora. The juvenile form possesses plagiotropous shoots the 

 leaves of which adpressed to the tree-stems cover the roots, but non- 

 rooting shoots arise later which are either orthotropous or at least stand out 

 from the substratum and bear stalked larger leaves, and it is upon these 

 that the flowers arise 3 . Some climbing species of fig, Ficus scandens and 

 F. pumila for example, exhibit like features and in our plant-houses we 

 see them almost always in their plagiotropous juvenile form. 



The juvenile form shows in all these plants an evident adaptation which 

 has arisen in conjunction with their climbing mode of life, and we see the 



1 The history of the ivy leads me to doubt the general validity of this statement; at least 

 it is difficult to see why such a difference should ensue. 



2 I have often had sent to me by nurserymen the juvenile form of an aroid as a Marcgravia. 

 Some of the Marcgravieae seem to have no juvenile form, for example, Norantea guianensis. 



' The different forms of leaf differ anatomically. Upon the under side of the leaves of plagiotropous 

 shoots there is a relatively thick air-tissue into the inter-cellular spaces of which water is perhaps 

 frequently injected, and it forms a protective covering to the roots. If the plant grows upon 

 a thin supporting branch the surface of the leaf curves round in correspondence with the surface of the 

 branch. As in the climbing aroids referred to in the text the juvenile leaves in Marcgravia are 

 distinguished by their ' velvety ' character ; a drop of water placed on the leaf rapidly disperses. 



