128 



OSMUNDACEAE 



[CH. 



The former is characteristic of Osmmida and Todea barbara, and it is pro- 

 bably a primitive feature (Chapter II, p. 40). The latter is seen in Lcptopteris, 

 and is the basis of its distinction as a genus. Here there is a thin pellucid 

 structure of the pinnules. It is, however, a question whether the difference 

 deserves generic value, since it is probably a relatively late adaptation to 

 life under conditions of excessive moisture. It is found in species from 

 Australasia, and the South Sea Islands. The pinnules, which are cut into fine 

 segments, each with a single vein, approach in their filmy structure that of 

 the Hymenophyllaceae (Fig. 417). 



Fig. 417. Juvenile leaf ot" Leptopteris {Todea) superba, 

 showing single-nerved segments all separate. ( x 3.) 



Certain deviations from the normal development of the shoot in Osminida 

 regalis have recently been described by Prof Lang; they seem to bear 

 a definite comparative interest. They followed on conditions of disturbed 

 development acting on young plants, and they resulted in transitions of what 

 can only be regarded as leaf-rudiments into shoots. Two examples are 

 quoted in Fig. 418, A, B. In one of them {A) a bud appears on the ventral 

 face of a leaf (<$-), both being supported on a common stalk: in the other (/)) a 

 leaf is represented by a cylindrical structure, of a deep green colour, which 

 ends without any lamina in a bud ib). Such indeterminate members, neither 

 typically leaf nor bud, have an interesting relation to the morphological 

 question as to the real nature of these parts. This interest is considerably 

 increased by the fact that similar indeterminate states have been found in 

 plants of Plagiogyria grown under natural conditions in the open (see 

 Chapter xxxi). 



In Todea there is no marked difference between sterile leaves and 

 sporophylls, and the sporangia appear on the under surface of leaves not 



