4 o8 PRO TOPH VTA 



While the Schizophyceas or chlorophyllous Protophyta approach very 

 closely to the lowest forms of Algae, the Schizomycetes or non-chloro- 

 phyllous Protophyta exhibit greater affinities, as de Bary has shown, with 

 the chlorophyllous forms than with any family of Fungi, Grouping,, 

 therefore, all these lowest forms of vegetable life, whether containing 

 chlorophyll or not, into a single subdivision of Cryptogams, it will be 

 most convenient to discuss them under two heads, as distinct and to a 

 certain extent parallel series. 



GROUP I. SCHIZOPHYCEyE. 



An attempt is here made to bring together those chlorophyllous; 

 forms which, in the present state of our knowledge, we must regard as- 

 primordial ; while others, almost equally simple in structure, have been 

 referred to the classes of which they appear to be retrogressive members. 

 The group now under consideration comprises the greater number of the 

 forms of vegetable life which are unicellular, which display no true pro- 

 cess of sexual reproduction, and which contain chlorophyll. 



Limited in this sense, the Schizophyceae may be divided into three 

 well-marked classes, the Protococcoide^ the Diatomacecz, and the Cyano- 

 phycece. In the Cyanophyceae are included those forms in which the 

 pure green colour of the chlorophyll is masked by a blue-green pigment 

 dissolved in the cell-sap, an arrangement not found except in plants of 

 the very simplest structure. The position of the Diatoms has been a 

 subject of much controversy among systematists. They display in 

 some respects a similarity to the Desmids ; but, for reasons given below, 

 we are disposed to consider this resemblance as apparent rather than 

 real, and to regard the Diatomaceae, not as a family derived from the 

 Desmidiaceae by retrogression, but as a primordial type of great simplicity 

 of structure. In the Protococcoideae are included those forms in which 

 the pure-green of the chlorophyll is not concealed by the blue-green 

 colouring matter of the Cyanophyceae, nor by the brown colouring 

 matter of the Diatoms. It is unquestionably from them that all the 

 higher forms of vegetable life have been derived, and the boundary line 

 between the Protococcoideae and the lower forms of Algae is one that 

 cannot be accurately laid down. 



LITERATURE. 



The literature of the Schizophycese is included under that of Algae, or in the 

 works specially named when treating of the separate classes and orders. 



