2o8 ■ DIPTEROID FERNS [CH. 



Platycerium and Cheiropleiiria in close relation, with a pointed reference to 

 Dipteris {Farnkr. p. 128). Such divergent expressions of opinion will serve to 

 stimulate interest in the examination of these remarkable plants. 



Platycerium is represented by some 14 species, which are all tropical 

 epiphytes: the genus extends to both eastern and western hemispheres, 

 but chiefly in the Malayan area. The habit, with its nest-leaves appressed 

 to the tree trunk on which the plant grows, and the erect or pendant 

 "foliage-leaves" which habitually bear the sori, is familiar from text-books, 

 and from the specimens commonly grown in greenhouses : so that the specific 

 details need not be described here (compare Vol. I, Fig. 54). It may suf- 

 fice to say that revision of the large series of specimens in the herbarium 

 at Kew confirms very strongly its Dipteroid character both in form and 

 venation of the leaves, and notably in their bifurcate branching. How 

 near the similarity of the erect leaves may be to those of Cheiropleiiria 

 will be seen from comparison of the photographs represented on Fig. 709. 

 Von Straszewski has traced the development from the sporeling: he 

 finds the first leaves to be upright, and of simple form, with a single vein: 

 the third leaf is round or kidney-shaped, with reticulate venation (com- 

 pare Fig. 711, B, above), and it is furnished with the usual stellate hairs. 

 The creeping stem bears the later leaves in bi-seriate order upon its upper 

 side. They are differentiated at once as nest-leaves and erect or foliage- 

 leaves: but the two types do not follow in any constant sequence. In close 

 relation to the erect leaves, lateral buds arise from the stem, and their 

 vascular supply has been found to spring from it. These relations appear 

 to resemble those of Cheiropleiiria and Lophosoria. The soral patches which 

 usually appear on the underside of the erect or pendant foliage-leaves, are 

 of irregular outline, and sometimes they are borne on special leaf-lobes 

 {P. coronariiim). These fertile areas may attain very large size: on a speci- 

 men in Kew of P. grande (Cunn.) J. Sm., from Singapore, it is more than 

 a foot across. But fertility is not restricted to the "foliage-leaves": Poisson 

 has recorded the production of sporangia on the nest-leaf of a Platycerium 

 grown in Paris (Von Straszewski, I.e. p. 300). This fact suggests that the 

 two types of leaf have differentiated from a common prototype, which may 

 have been not quite like either of them. Such a prototype probably re- 

 sembled the homophyllous leaves of the Dipteroids. I see no sufficient reason 

 for regarding the nest-type of leaf as the more primitive. 



In Ferns so highly specialised as Platyceriiiiii, and of a rather gross 

 habit, it is natural to anticipate that there will be a disintegrated vascular 

 system: and that is what examination shows. Even in the sporeling we 

 need not look for structure of a strict type : nevertheless, the sporeling, 

 after a short protostelic stage, passes to a condition with a solenostele 

 interrupted only by the departure of the leaf-traces (Von Straszewski, I.e. 



