CHAPTER XLV. 



THE SPORE-PRODUCING MEMBERS. 



So far only the vegetative organs have been considered in this summary 

 of results ; the reason for this is that they appear the first in the individual 

 life of Vascular Plants, and it is only after the vegetative system of the 

 sporophyte has been established that spore-production supervenes. The 

 relation of the sterile to the fertile region from the point of view of 

 descent has, however, been discussed at length in Chapter XIII. : the 

 conclusion was there reached that in vascular plants the sterile 

 tract, which is prior in the individual life, is itself from the evolutionary 

 point of view, the consequence of a secondary change, since the foliage 

 leaves are themselves held to be sterilised sporophylls. In Chapter XIV. 

 it was further concluded (p. 186) that there existed initially only one 

 type of leaf the sporophyll, and that even the protophylls are the 

 result of their transformation. Moreover, justification for this is found 

 in the positive fact that spore-production occurs very early in certain 

 plants (Ophioglossaceae and some Lycopods), while in Lygodiiun subalatuin 

 the extreme condition was actually observed by Prantl, viz. that the 

 primordial leaves are themselves fertile sporophylls. With these facts, and 

 this general conclusion before us, we may now proceed to consider the 

 morphology of the spore-producing members and their relation to the 

 other parts of the shoot. 



On an antithetic theory of origin of the sporophyte we contemplate 

 an initial condition of a simple body having a coherent group of spore- 

 mother-cells, provided, in fact, with a simple spore-sac. The Bryophytes, 

 with their concrete archesporium, retain this state even in their more 

 advanced forms ; but the Vascular Plants, with their discrete sporangia, 

 have diverged from it very widely. The two types of construction are 

 not connected by any living intermediate links, nor is there any direct 

 proof that the one type is phyletically related to the other. But both 

 provide evidence suggestive of how a segregation of spore-mother-cells 

 into distinct sporogenous masses, such as appear in the separate sporangia, 



