METAMORPHOSIS IN PLANTS. 99 



leaf-organs, that the plant, as a matter of fact, gives origin 

 to leaves of one kind only, namely the foliage-leaves, the 

 ultimate form of which is modified in various ways by 

 conditions which arise in the course of their subsequent 

 development ". Whilst Goebel agrees with his predecessors 

 in regarding the foliage-leaf as the material basis of meta- 

 morphosis, it appears that there is a difference between 

 them as to the mode of the process : according to the older 

 view the more highly modified organs are the products of 

 mediate metamorphosis of the foliage-leaf ; the stamen, for 

 instance, being traceable to it through the petals and 

 sepals : Goebel, on the contrary, asserts that metamor- 

 phosis is immediate, regarding all other forms of leaves as 

 being directly traceable to the foliage-leaf, though they may 

 be sometimes transformed into one another. 



The view that the foliage-leaf is the primitive leaf- 

 member, and that the floral leaves are its derivatives, is then 

 based upon the fact that, as a rule, the vegetative precede 

 the reproductive organs in ontogenesis. The opposite view 

 that the most highly specialised floral leaf, the sporophyll, is 

 the primitive phyllome, is based upon the fact that, phylo- 

 genetically, the reproductive precede the vegetative leaves. 

 The full discussion of the latter view would involve an 

 amount of technical detail which would be altogether out 

 of place in such a lecture as this. I must content myself 

 with briefly explaining that in such lowly organised plants 

 as the Mosses (Bryophyta), the sporophyte, that is the 

 form in the life-history which correspond to the Flowering- 

 plant, consists,' in the simplest case, of little more than a 

 mass of reproductive cells ; and even in the more complex 

 Mosses, this form never presents any differentiation of vege- 

 tative organs. We find, then, that in such primitive plants 

 as the Mosses, the reproductive is the predominant function. 

 Turning now to the Fern-like plants (Pteridophyta), the 

 plants which come next above the Mosses, we find that 

 they have well-developed leaves ; and further, that in the 

 more primitive forms the leaves are distinctly differentiated 

 into sporophylls and foliage-leaves ; whereas in what may be 

 regarded as the secondary forms, this distinction is either 



