232 THE SPORE-PRODUCING ORGANS [ch. 



and that by these they are naturally related to other well-known types. 

 Increasing knowledge of their anatomy confirms this, and developmental 

 study has demonstrated that the non-soral acrostichoid state does not in itself 

 indicate any real affinity of the plants which show it (Frau E. Schumann, 

 Flora, 191 5, p. 201, Studies, IV, VI, Vli). It is now clear that the spread of 

 the sorus and loss of its individuality have involved derivatives from at least 

 six well-known types. It has been shown {Studies, iv) that Steiwchlaena 

 and Brainea may be traced as derivatives from the Blechneae by such a 

 spread of sporangium-formation over the leaf-surface (Fig. 230). Similarly 

 AcrosticJiuui praestantissiuiuvi and aureuin may be referred to the Pterideae: 



Fig. 230. \'eitical sections through fertile pinnae of Stenochlaena 

 soj-bifolia, with the lower, fertile surface directed upwards. 

 (X125.) 



Syngramvie and Elaplioglossuui to the Metaxyeae: Trisnieria to the Gymno- 

 gramminae: Polybotrya and ^/^«(5'j'^;«z« to the Aspidieae : and CJieiropleuria, 

 Leptochilus tricuspis and Platyceriwn to the Dipteridinae. Other Acrostichoid 

 species described under the name of Leptochilus are referred by Frau Schu- 

 mann to an origin from Meniscium, and to certain species of Polypodium 

 {Flora, 191 5, p. 222, etc.). 



The Acrostichoid derivatives of the Dipteridinae present a peculiar feature 

 in the vascular supply to their fertile region. In most Acrostichoids there is 

 no special vascular provision for the nutrition of the sporangia. But in the 

 Dipterid-derivatives it is different. Their condition appears to be arrived at by 

 an elaboration of the sorus, which meanwhile maintained its individuality and 



