94 Morphology BOOK I 



sity of looking for its homologues among stems and leaves, 

 and opened the way to the comparison of the ovule and the 

 structures which it contains with other structures occupying 

 similar positions in the life-history of the Pteridophyta, and 

 so to the establishment of true homologies extending 

 through the range of vascular plants, both recent and 

 extinct. 



In 1860, and for some years subsequently, the accepted 

 view of the morphology of the ovule was the pronouncement 

 of Schleiden and Braun that the placenta is an axial 

 structure, and the ovule arises as a bud upon it. The 

 integuments of the ovule thus correspond to the fused 

 leaves of such bud. 



Though this was the opinion of most botanists of the time, 

 it was not felt to be satisfactory, and two other hypotheses 

 were developed in the course of the next decade. In 1869 

 a theory which had been held by a few morphologists even 

 before 1860 was restated by Cramer. It was that the ovule 

 is a metamorphosed leaf or part of a leaf, either a tooth 

 or an outgrowth of the upper surface. Sachs states 

 Cramer's position in the Lehrbuch in the following terms : 

 1 The ovule of Primulaceae and Compositae he considered 

 to be a whole leaf, and he supposed that closer observation 

 would show the same to be the case in other flowers also, 

 especially in those where the flower is said to possess a 

 solitary ' reputed terminal ovule ' as Urlica (and Taxus) 

 and perhaps also the Dipsaceae and others. The nucleus 

 (nucellus) would in this case be a new formation on the 

 surface of the ovular leaf, the funiculus would correspond 

 to the base of this leaf, and the integuments to its upper 

 part, which is folded once or twice in the form of a cup or 

 hood round the nucellus. On the other hand, he would 

 consider as only portions of the leaf (teeth or outgrowths of 

 the upper surface) all those ovules which spring singly or 

 in numbers from the margin or upper surface of carpellary 



