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. e 
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 
