CHAPTER XIII. 



ON THE RELATIONS BETWEEN THE STERILE AND 

 FERTILE REGIONS IN THE SPOROPHYTE. 



FROM the days when Morphology first arose as a branch of the science 

 of Botany, the relations between the sterile or vegetative region of Plants, 

 and the fertile or reproductive have been the subject of enquiry. Originally 

 the question presented itself as one of simple comparison of those regions 

 in the Flowering Plants, in which they are clearly differentiated one from 

 another : the basis of the comparison was that of their external form, 

 with the idea behind it of some degree of unity of plan in the construction 

 of the two regions. At the present time the enquiry involves the direct 

 question of their physiological relation, but it also extends to the indirect 

 historical problem of their genetic relationship. This can best be approached 

 by comparison of forms lower in the scale of development, such as the 

 Pteridophytes, in which the differentiation is less complete than it is in 

 the Flowering Plants. 



From a physiological point of view, the necessity of a due balance 

 between the sterile and fertile regions in the case of any fully differentiated, 

 self-supporting organism is readily grasped; for the material required to 

 build up the strobilus or flower to the point of maturing its spores must 

 be derived from an adequate development of the vegetative organs which 

 produce it. It is naturally otherwise in sporophytes which are not self- 

 supporting, or only partially so, as in the Liverworts and Mosses : also 

 in the case of parasites and saprophytes ; but the latter, as derivative or 

 secondary conditions, may be put aside when we discuss the adjustment 

 of balance between the two regions in its evolutionary aspect. The 

 indirect historical question is less readily tangible, but in its solution the 

 sources of nutritive supply must be steadily kept in view throughout the 

 comparative study of the lower and simpler sporophytes. 



The fact that there is frequently a tendency towards extended production 

 of spores in the Homosporous Archegoniatae has been brought forward 

 repeatedly in previous chapters, where also the racial advantage which 



