IX 



FILICINE^ LEPTOSPORANGIAT^ 



309 



pidium aiix-mas var. cristatum, Aspidhim falcatiim, Todea 

 Africana, and several others. Sometimes archegonia are pro- 

 duced, or they may be absent from the apogamous prothalHum, 

 but antheridia usually are found. When archegonia are 

 present they do not appear to be functional. In Pteris Cretica 

 (Fig. 171, A), where usually no archegonia are developed, the 

 cushion of tissue which ordinarily produces them is formed as 

 usual ; but instead of forming archegonia it grows out into a 

 leaf at whose base is formed the stem apex, w^hich soon pro- 

 duces a second leaf. The first root arises endogenously near 

 the base of the primary leaf, and the young plant closely resem- 

 bles the sporophyte produced in the normal way. Previous to 

 the development of the bud there 

 is formed in the prothallium it- 

 self a vascular bundle which is 

 continued into the leaf, but 

 is entirely absent from normal 

 prothallia. 



The opposite state of affairs, 

 where the gametophyte arises di- 

 rectly from the sporophyte with- 

 out the intervention of spores, is 

 known in a number of species, 

 and has been especially investi- 

 gated by Bower (6). He found 



that there were two types of Fig. 172.— Pinna from the leaf of Cys- 



^ J , topteris bulbifera, with a bud ik) 



apOSpOry, as he named the ^t the base, X2; s. the sori (after 



phenomenon, one where the pro- Atkinson). 

 thallium was produced from a 



sporangium arrested in its normal growth, and by active multi- 

 plication of the cells of the stalk and capsule w^all forming a 

 flattened structure, which soon showed all the characters of a 

 normal prothallium with sexual organs. In the second case the 

 prothallia grew out directly from the tips of the pinnae, and 

 there was no trace of sporangia being formed previously. The 

 first observations of these phenomena w^ere made upon two 

 varieties, Athyrhim iilix-focmina var. clarissima and Poly- 

 stichum angular e var. pulcherrinmm, but since, Farlow^ (2) has 

 discovered the same phenomenon in Pteris aquilina. In the 

 latter the prothallia were always transformed sporangia. The 

 phenomenon of apospory was first observed by Druery ( i, 2). 



k.- 



