364 CHARACTERS OF THE HIGHER PLANTS LESS. 



always protected by a root-cap, that of the stem being simply 

 over-arched by leaves. Moreover an alternation of genera- 

 tions can be traced in all cases. 



Plants may be conveniently divided into the following 

 chief groups or phyla : 



Alga. 



Fungi. 



Muscinea. 



Vascular Cryptogams. 



Filicinae. 



Equisetaceae. 



Lycopodineae. 

 Phanerogams. 



Gymnosperms. 



Angiosperms. 



The Alga are the lower green plants. They may be 

 unicellular, or may take the form of linear, superficial, 

 or solid aggregates : they never exhibit more than a 

 limited amount of cell-differentiation. This group has been 

 represented in the foregoing pages by Zooxanthella, diatoms, 

 Vaucheria, Caulerpa, Monostroma, Ulva, Laminaria, and 

 Nitella. 1 



The Fungi are the lower plants devoid of chlorophyll : 

 some are unicellular, others are linear aggregates : in none 

 is there any cell-differentiation worth mentioning. Saccharo- 

 myces, Mucor, Penicillium, and the mushroom belong to 

 this group. 



The position of some of the lower forms which have come 

 under our notice is still doubtful. Bacteria, for instance, 

 are considered by some authors to be Fungi, by others Algae, 



1 By some authors Nitella is placed near the Muscinea:. 



