PLANT MORPHOLOGY 75 



thinking that all the primitive leaves in certain types, such as the 

 lycopods, were sporophylls, and that a subsequent differentiation 

 took place, by abortion of the sporangia: thus a sterile vegetative 

 region became defined from a fertile upper region. It may be a 

 question whether this origin by sterilization of sporophylls is appli- 

 cable to foliage leaves at large: nevertheless analogy, not only with 

 other vascular plants, but also with the bryophytes, suggests that 

 a similar differentiation of a sterile from a fertile region has been a 

 general phenomenon in the neutral generation. At first in the simpler 

 pteridophytes these regions were essentially similar to one another 

 in form, as is still seen to be the case in some lycopods. Later, 

 however, the sterile and fertile regions took divergent lines of de- 

 velopment in accordance with their difference of function. The 

 differentiation reaches its climax in the higher flowering plants. 

 The inflorescence, or flower, on this view, though produced later than 

 the vegetative region in the individual life, embodies the more 

 primitive parts, viz., those which bear the sporangia and spores; 

 the vegetative region is in its origin mostly, if not wholly, secondary. 

 The physiological reasonableness of this view is too obvious to need 

 insistence. As the self-nutritive powers of the gametophyte fell off 

 in the adaptation to the land-habit, the nutritive function was taken 

 up by the new vegetative system thus intercalated between sexual 

 fusion and spore-production. 



This is in brief outline the strobiloid theory of the shoot in vas- 

 cular plants, as arising out of the facts of antithetic alternation. 

 It will be seen that it is essentially in harmony with the view of 

 Braun, upheld also by Sachs, that the shoot is the real morphological 

 unit, of which leaf and axis are correlative parts. Those who adopt 

 it will find their position simplified in regard to another question 

 which has recently taken afresh a prominent place in morphological 

 discussions, viz., the theory of cortication (Berindungstheorie). It 

 is held by Potonie", and a similar view was also maintained by 

 Celakovsky, that the stem has centrally an axial nature, peripherally 

 a leaf-nature. The primitive axis (Urcaulom) acquires in the course 

 of generations, by coalescence with the basal parts of its primitive 

 leafy appendages (Urbldtter), a mantle, a "Pericaulom." This is 

 what we commonly designate the cortex, which is thus regarded 

 as not being axile in origin, but foliar. In accordance, however, 

 with our strobiloid theory, we may presume that, as is seen in some 

 of the bryophytes, the simple sporophyte consisted originally of a 

 central region, a primitive stele, and a peripheral region, a 

 primitive cortex. From the latter sprang the appendages, as super- 

 ficial outgrowths, just as at the present day the leaves originate 

 upon the cortex of the axis. The cortex in such cases would be, from 

 the first, part of the primitive axis, and the outgrowths processes 



