MB. P. O. BOWEE ON APOSPOBT IN TEENS. 303 



A point worthy of note is, that in those prothalloid structures 

 which are taken directly from living leaves in the normal position 

 without further cultivation, the antheridia and archegonia have 

 not opened ; no doubt this is due to the want of water, which, as 

 is well known, is necessary for this process. I have not yet been 

 able to observe the formation of young Pern-plants on these 

 prothalli ; but it may be hoped that from cultures now in pro- 

 gress at Kew and elsewhere further evidence may be obtained 

 on this point. 



This Polystichum is thus an example of the formation of an 

 expansion of undoubted prothalloid nature, bearing sexual organs 

 by a process of purely vegetative outgrowth from the Fern-plant; 

 that is, there is a transition in this case from the sporophore 

 generation to the oophore by a vegetative growth, and without 

 any connection either with spores or, indeed, with sporangia or 

 sori. It may be regarded as a still more complete example of 

 apospory than that of Athyrium Filix-fcemina, var. clarissima. 



It remains to point out the bearing of these observations upon 

 the general life-history of the Fern. The normal cycle of life of 

 these plants may be represented graphically thus : — 



Diag. 1. 



Spore „ ^ . 



a Sporangfiim< 



Prol/t^dlus 

 or Oophore 



Sporophore 

 orFernHaxt 



Sexual 



Organs 



We already know various modifications of this simple cycle, 

 which may be classified under two heads : — 



1. Modifications which lengthen the cycle. 



2. Those which reduce it, and may therefore be regarded as 

 short cuts. 



Taking first those of the first category, they may be described 

 as modes of vegetative reproduction, by which one generation or 

 the other simply reproduces itself. Thus the sporophore, or 

 Fern-plant, may form adventitious buds, which are found seated 



