2.] CHAPTER I. GENERAL MORPHOLOGY. 7 



plants is differentiated into stem and leaf at some stage of development, though 

 not in the adult stage ; in many such plants, members which accord with the 

 preceding definition of the leaf are present, though they do not present the 

 appearance characteristic of foliage-leaves. 



The root never bears true (spore-producing) reproductive organs. 

 Like the stem, it is an axis, and it is co-ordinate with the stem 

 in structure, but it does not bear leaves, and its structure presents 

 certain characteristic peculiarities. 



It occasionally happens that one member may directly assume 

 the characters of another. Thus, stems sometimes assume the 

 form of foliage-leaves ; and roots have been observed to bear 

 leaves, becoming, in fact, leafy shoots, in Anthurium longifolium 

 and Neottia Nidus- Avis. 



2. Symmetry of the Body and of the Members. 

 Whatever the form of the body or of a member, it has three axes 

 at right angles to each, other. When these are all three equal, 

 the body is a sphere (Haematococcus, Volvox, etc.) ; when two are 

 equal, and both longer than the third, the body or the member is 

 a flattened circular expansion (e.g., Pediastrum, Coleochcetescutata); 

 when one is longer than either of the others, the body or the 

 member is cylindrical or prismatic when the two shorter axes are 

 equal, and flattened when one of the shorter axes is longer than 

 the other. 



In most cases two opposite ends are distinguishable in the body 

 or member, a base and an apex. The base is in all cases the end 

 by which the body is attached to the substratum, and the 

 members to each other, the free end being the apex. The axis 

 joining the base and the apex is distinguished, whether or not it be 

 longer than the other axes, as the organic longitudinal axis. When 

 the body has no distinction of base and apex, there is no organic 

 longitudinal axis ; but in cases of this kind (e.g. the filaments of 

 Spirogyra) the longest axis is taken as the longitudinal axis. 



Any section, real or imaginary, made parallel to the longi- 

 tudinal axis, is a longitudinal section; it is a radial longitudinal 

 section if it includes the longitudinal axis ; it is a tangential longi- 

 tudinal section if it does not include it. A section made at right 

 angles to the longitudinal axis is a transverse section ; the section 

 of the longitudinal' axis is the organic centre of the transverse 

 section, and it commonly is also the geometrical centre of the 

 transverse section, but occasionally the organic and the geometrical 

 centres do not coincide. Thus, in transverse sections of tree-trunks, 



