306 BOTANY 



exceptionally provided with such a pigment, live either parasitically 

 or saprophytically, and may be regarded as a derived form of 



Schizophyceae. 



Order 1. Schizophyceae (Fission- Algae) 



The Fission- Algae were formerly thought to show a variation from 

 other Algae in the differentiation of their cells. It was customary to 

 distinguish within the protoplasts of their walled cells an apparently 

 homogeneous colourless central-body, separated from the other portion 

 of the cell contents by a delicate membrane, and possessing a greater 

 capacity for taking up stains. According to the recent investigations 

 of Heglbr, this central body has, however, the structure of a true 

 nucleus, and undergoes indirect karyokinetic division. In certain of 

 the filamentous forms, special cells, no longer capable of division, may 

 contain several nuclei, the number of which is in such cases the 

 result of fragmentation. The cell nucleus is surrounded by a coloured 

 peripheral layer. This layer may be considered as equivalent to a 

 chromatophore ; it contains, in addition to chlorophyll, a blue-green or 

 verdigris-coloured pigament, termed phycocyanin, to the presence of 

 which this group of the Schizophyta owes its name of Cyanophyceae 

 or Blue-green Algae. There are also found within the cells, usually 

 lodged in the periphery of the chromatophores, small granular bodies 

 of an unknown significance, the so-called cyanophycin grains ; while 

 mucous globules are also disposed in the vicinity of the nucleus. In 

 addition to these, vacuoles occasionally occur in the cells. The cell 

 walls consist of cellulose, and often exhibit distinct stratification, and 

 in many species they undergo a mucilaginous modification of their outer 

 layers. Multiplication is effected in a vegetative manner, simply by 

 the division of the whole contents of the cells and by the formation of 

 partition walls. In the case of the unicellular forms, included col- 

 lectively in the family of the Chroococcaceae the daughter cells separate 

 after the division, and become either entirely isolated or remain as 

 cell colonies in proximity with one another. In the filamentous forms 

 or Nostocaceae, the daughter cells continue in contact and form cell 

 rows. These cell filaments eventually break up into shorter segments, 

 which repeat the process of multiplication and segmentation. It is 

 from this mode of reproduction by the division or fission of the cells 

 that the name Fission-Algae has been derived. 



The Fission-Algae represented by numerous species are universally 

 distributed. They occur as floating water forms, attached to stones 

 and plants, or they form mucilaginous or pubescent coatings on damp 

 soil, moist rocks, tree-trunks, moss, etc. 



1. Chroococcaceae. — The simplest forms of the Schizophyceae are included in this 

 family. The genus Ghroococcus consists solely of isolated, rounded cells, which 

 are enveloped by a thin wall and have a blue-green colour. In other genera cell 



