O. THE SEGMENTATION OF THE BODY. O 



the Pteridophyta, the sporophyte is the plant such as we know 

 it, whilst the gametophyte is so much reduced that it may be 

 regarded as an appendage upon the sporophyte. Thus, in tracing 

 the morphology of the two generations from the Bryophyta 

 upwards, the relations between them are gradually reversed ; so 

 that the higher the plant is in the scale of organisation, the more 

 conspicuous is its sporophyte, the less conspicuous 'its gametophyte. 



The following pages refer mainly to the morphology of the 

 sporophyte of the higher plants, that is, of the Pteridophyta and 

 Phanerogamia, except when the gametophyte or one of the 

 Bryophyta or Thallophyta is especially mentioned. 



3. The Segmentation of the Body. The body of a plant 

 may be either segmented into members, or unsegmented. The 

 members of a segmented body may either be all similar, or they 

 may be similar and dissimilar. Segmentation into similar mem- 

 bers is termed branching. When the body is segmented into 

 dissimilar members, it is said to be morphologically differentiated. 



When the body is morphologically undifferentiated, that is, 

 when it is either unsegmented or segmented only into similar 

 members (i.e. branched), it is termed a thallus. A Thallophyte is 

 a plant having a body of this constitution and of simple structure 

 (e.g. Yeast, Spirogyra). 



The primary segmentation of the body into dissimilar members 

 consists in the differentiation of root and shoot. 



The Root is usually segmented, but only into similar members. 

 It occasionally gives rise to (adventitious) shoots. 



The Shoot may be either unsegmented, or segmented into similar 

 or dissimilar members. A shoot which is either unsegmented, 

 or segmented only into similar members, is termed a thalloid shoot 

 (e.g. Lemna, the Duckweed). A shoot which is segmented into dis- 

 similar members consists generally of stem and leaves. 



The characteristics of the principal members are as follows : 



The shoot bears the true (spore-producing) reproductive organs : 

 it is generally differentiated into stem and leaf. 



The stem is the axial member of the shoot, and bears the leaves. 



The leaf is the lateral member of the shoot : it is borne upon the 

 stem, but differs from it more or less in form. 



The root never bears leaves or true (spore -producing) reproduc- 

 tive organs. 



The hair is an appendage which may be borne on either root, 

 stem, or leaf. 



