4 PART I. THE MORPHOLOGY OF PLANTS. 



has been given, and on which classification is based, in the Mosses 

 and the plants below them, it is to the gametophyte that the name 

 has been attached, and it is upon its characters mainly that the 

 classification of these plants depends. 



At this point the question naturally arises as to the morphological 

 relation, if any, which may exist between the members of a game- 

 tophyte and those of a sporophyte. Since, speaking generally, the 

 morphological differentiation of the one form has proceeded along 

 the same lines as that of the other, a certain correspondence exists 

 between their members. For instance, a foliage-leaf of a Moss 

 (gametophyte) corresponds to that of a Fern (sporophyte) ; for, 

 in the forms to which these leaves respectively belong, they 

 stand in essentially similar relations, both of development and 

 position, to the other members of the body. But the corres- 

 pondence does not amount to relationship, and cannot be regarded 

 as constituting homology as defined above (p. 1). It is, however, 

 permissible, to this extent, to institute comparisons between the 

 various members, reproductive organs, etc., of the two generations. 



The consideration of the polymorphism of plants is a most 

 important preliminary to the study of their morphology, inasmuch 

 as this knowledge facilitates precision of statement, and prevents 

 that comparison of like with unlike which has been so common 

 in this department of Botany. For instance, since the sporophyte 

 and the gametophyte of one and the same plant are generally very 

 different from each other, it conduces to clearness if, when 

 reference is made to the morphology of any plant, it be de- 

 finitely stated to which form of it the reference applies. And 

 again, it is impossible to institute sound morphological comparisons 

 between the members of different plants unless it is clearly under- 

 stood to which form, whether sporophyte or gametophyte, the 

 members to be compared belong in each case. 



The most fundamental preliminary consideration is, however, 

 this that the body of a plant consists essentially of a mass, larger 

 or smaller, of living substance known as protoplasm. The body 

 may consist simply and only of protoplasm, without any investing 

 membrane to give it a determinate form (e.g. Myxomycetes) ; or 

 it may consist of protoplasm enclosed by a membrane (e.g. Phyco- 

 myoetous Fungi and Siphoiiaceous Algae) ; or it may consist, as 

 is generally the case, of a mass of protoplasm segmented by par- 

 tition-walls into structural units termed cells. In all these 

 possible cases, however, the form and segmentation of the body 



