532 



SCIENCE. 



[N. S. Vol. XX. No. 512. 



the ease in the calamarian strobilus, where 

 the leaf tooth can not be readily homolo- 

 gized with the sporangiophore. These sug- 

 gestions will suffice to indicate how elastic 

 & strobiloid theory is, and how its applica- 

 tion will cover various types of construc- 

 tion, even such as are shown by the most 

 complex cones of pteridophytes. 



From the comparison of living species 

 there is good reason for 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 applicable to foliage leaves 

 at large. Nevertheless, analogy, not only 

 with other vascular plants but also with 

 the bryophytes, suggests that a similar dif- 

 ferentiation of a sterile from a fertile re- 

 gion 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 development in accord- 

 ance 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 in- 

 dividual 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 gameto- 

 phyte fell off in the adaptation to the land 

 habit, the nutritive function was taken up 

 by the new vegetative system thus inter- 

 calated between sexual fusion and spore 

 production. 



This is in brief outline the strobiloid 

 theory of the shoot in vascular plants, as 

 arising out of the facts of antithetic alter- 

 nation. It will be seen that it is essentially 

 in harmony with the view of Braun, up- 

 held 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 re- 

 cently taken afresh a prominent place in 

 morphological discussions, viz., the theory 

 of cortieation (Berindungstheorie). It is 

 held by Potonie, and a similar view was 

 also maintained by Celakovsky, that the 

 stem has centrally an axial nature, peri- 

 pherally a leaf nature. The primitive axis 

 (Urcaulom) acquires in the course of gen- 

 erations, by coalescence with the basal 

 parts of its primitive leafy appendages 

 (Urblatter), 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 ap- 

 pendages, as superficial 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 out- 

 groAvths processes from it. The primitive 

 cortex from which the appendages sprang 

 may remain a continuous, undifferentiated 

 band, as it actually does appear in the 

 vast majority of leafy sporophytes; or 

 it may be in certain cases more or 

 less clearly marked off into regions sur- 

 rounding the insertion of the individual 

 leaves. But in the fact that these special 

 eases exist I see no sufficient foundation 

 for the view that each leaf is, in shoots at 



