208 GENERAL CHARACTERS OF CRYPTOGAMS 



the leaves are rudimentary in ditt'erent degrees, from those which 

 want only the most perfectly develoi)ed leaf-structure to those which 

 are mere scales, consisting of a single layer of flattened cells. By far 

 the greater number, comprising the lower classes, have nothing which 

 can be described as homologous with the leaf, the plant consisting of a 

 simple body which, presenting many different kinds and degrees of 

 variation in form, habit, and function, yet never shows any indication 

 of the regularly jointed structure characteristic of the higher plants, 

 nor any leaves. 



Equally great is the variation observed among the roots. Many of 

 the higher forms possess true absorbing roots, but probably a great 

 majority of roots among Cryptogamous plants are false roots or rhizoids, 

 existing for purposes of fixation only. 



Lacking, as these plants do, the elaborate structures whose character- 

 istics have enabled us to identify, describe, and classify the higher 

 plants, we are obliged to look for such characteristics among the differ- 

 ent arrangements of their cells. Since this work requires the aid of 

 the compound microscope and considerable technical skill, entirely 

 new methods of examination become necessary. We do not, therefore, 

 find it practicable to consider them in detail here. 



The cellular structure of these plants may extend itself in the three 

 directions of solid bodies, giving us masses of tissue, or they may multi- 

 ply in two directions only, giving us flat or superficial bodies, or they 

 may be joined merely end to end, producing filamentous forms. These 

 bodies may each constitute a single plant, or their cells may cohere 

 merely by habit, each living equally well if separately detached ; or they 

 may normally live in a separated condition, thus giving us perfect plant 

 bodies, each consisting of but one cell, the unicellular plant. 



These imicellular plants, furthermore, vary most widely in their 

 own structural characters. They may be of microscopical size, or they 

 may become many feet in length. They may possess the simplest 

 structure, or they may develop large cavities, which are divided and 

 subdivided by processes developed from the wall, and be shaped into 

 remarkable forms, yet without true cell division or multiplication. 



Vegetation. — Regular vegetative processes are of course required 

 wherever growth occurs, wherefore we must look for them among even 

 the simplest forms. In many cases, these processes are as simple as the 

 bodies themselves. Absorption from a surrounding fluid medium by 

 the entire body of the plant, with the simplest of chemical transforma- 

 tions, may exist, or roots or other special organs of absorption, with 



