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THE GAMETOPHYTE, AND SEXUAL ORGANS 



[CH. 



prothalli oi Loxsoma and Dicksonia {¥\g. 268). But speculation on this point 

 cannot be fruitfully pursued until facts are available more numerous and 

 more cogent than at present (see von Goebel, I.e. p. 950, Figs. 939 — 941). 



Though commonly the apical growth arises from the distal end of the 

 primary germinal filament this is not always so. Von Goebel cites the case of 

 Pteris longifolia in which a spathula-shaped thallus is first formed (Fig. 267, A ) : 

 presently a meristem is established in one of the wings, often with an initial 

 cell, and forming a lateral lobe (Fig. 267,3). Later another lobe is formed in 

 like manner on the other side, but smaller {C). This illustrates the establish- 

 ment of apical growth at points on the margin other than the originally 



P'ig. 267. A, B = yo\xng prothalli of Pteris longifolia, showing the establish- 

 ment of a lateral growing point; C= older prothallus showing unequal 

 lobes, the larger was first formed, the smaller is the later lobe ; D — young 

 prothallus of Anogratnme chaerophylla, with a young archegoniophore 

 projecting from the side; E='a.\\ older prothallus seen from the side; 

 F= a prothallus derived from the tuberous archegoniophore of the previous 

 year, having already formed a new archegoniophore. All after von Goebel. 



distal end, a process which serves to explain the lop-sided form of many 

 prothalli. In particular it is in this way that the peculiar arrangement for 

 perennation in Anogramme chaerophylla finds its elucidation. A lateral 

 meristem is here established on one side, and a lop-sided prothallus results 

 (Fig. 267, D). Just behind the lateral meristem a tuberous archegoniophore 

 is produced, which burrows into the soil, and becomes stored with starch, etc. 

 (Fig. 267, E). In this state it can resist drying out, and in case an embryo is 

 already established, it can advance quickly when external conditions are 

 favourable. If there is no embryo a new prothallial flap may grow out from 

 it, which later produces a second archegoniophore {F), the perennation being 



