254 



8 



The reduction of the leaf downwards varies within the whole group from 

 being nearly 0, as in D. firma, to the long and very gradually narrowed leaf of 

 D. opposita. Some variation, especially in the number of reduced pinnæ, may be 

 found also in the single species; on the other hand the kind of reduction is rather 

 constant and, therefore, a good character of species. If this character, however, 

 were to be extended to mark a group of species, it would be less valid, and it 

 would be difficult by means of it to lind out the relationship of species, even though 

 several show a striking likeness as to the shape of lamina, which are otherwise 

 closely allied. In practice, however, one may very well defend using the shape of 

 the leaf as the first consideration, so much the more as some different types can 

 be pointed out to which the great majority of species can be referred. 



Ill 



IV 



/\ 



K 



Fig. 1. 



1. Is the type of Z). oUgocarpa and related species. Here tlie leaf narrows gradually but rather shortly : 

 there are rarely more than 4—5 pair of reduced pinnæ, of which the lowermost are auriculiform, 

 though rarely very small. Stem ])roportionall}' long. The diagnostic phrase for this type is: lamina 

 breve et gradatim attenuata. 

 I. Is the type of D. opposita and its relatives. Here the leaf narrows almost from the middle very 

 gradually through a great number of reduced pinnæ nearly to the base of the stem: the lowermost 

 pinnæ' auriculiform, often verj' small. Lamina lunge et gradatim attenuata. 



D pachyracltis and others. Almost as type I, with only few — 3—4 — pair of shortened pinnæ, 

 which, however, are very remote and the lowermost not far from the base of the stem, auriculi- 

 form. The leaf generally much broader than in the species of types I and 11. 



D. Sprengelii, D. nidis etc. The leaf below 1 — 2 pair of reflexed, somewhat shortened pinnæ sud- 

 denly narrows with 3— (i, rarely more, pairs of aui-iculiform (the upper) or glanduliform pinnæ; 

 the lower abortive pinnæ' are reduced to small wart- or tubercle-shaped protuberances without 

 parenchyma on the stem. — Lamina abrupte attenuata, pinnis infimis glauduliformibus 

 V. Here a few species, as Ü. Moritziana, D. Mosenii, I), atiovirens: as in type IV the leaf narrows 

 suddenly, but the lower reduced pinnæ are auriculiform, often hastate or bipartite. — Lamina 

 abrupte attenuata, pimiis infimis auriculiformibus. 



result that species of arid habitat have generally denser veins than those of humid habitat. As I can 

 hardly judge of the particular outer conditions under which the species examined by me grow, 

 I cannot refuse to accept it, but I do not think it probable that there is a great difference in the 

 growing-places of such species as D. pachyrachis and D, snpina on one side and D. Sprengelii and 

 l). nidis on the other. 



