238 University of California Publications. [Botany 



lime on dripping rocks, penetrate into the shells of various mol- 

 lusks, thrive equally well in fresh or in salt water, even when the 

 latter is concentrated ; in fact there is scarcely a habitat in which 

 they may not be found, where any other forms of chlorophyll- 

 bearing plants can exist. They even possess the power to with- 

 stand sudden changes in the environment. Lyngbyas growing in 

 salt water may be placed in fresh water without affecting their 

 growth, and will live for a long time if placed in distilled water. 



The phylogeny of this group has not been well worked out. 

 It is at present set off by itself with doubtful affinities, but the 

 very fact of its diversity of forms suggests several lines of de- 

 scent. Considered from the standpoint of external vegetative 

 characters, it approaches somewhat the Chlorophyceae at several 

 points. Some unicellular species of Cyanophyceae very closely 

 resemble some of the unicellular Chlorophyceae. The same is 

 true of some of the filamentous forms. And, finally, so closely 

 do some of the membranaceous forms of the two groups approach 

 each other, that one species (Prasiola Gardneri Collins) was 

 placed in the Chlorophyceae until my cytological investigations 

 showed that it belongs to the genus Merismopedia of the Cyano- 

 phyceae. 



Interest is aroused in the cytologist by the group because in 

 it he hopes to discover some clue to the origin of the cell-nucleus. 

 A number of investigators of the group have turned their atten- 

 tion in this direction, and a variety of opinions has arisen con- 

 cerning it. These cytological studies have also revealed the pres- 

 ence of a variety of structures in the protoplast upon which 

 various interpretations have been placed. The questions of prin- 

 cipal interest are : First, Is there a nucleus or not 1 Second, If 

 there is a nucleus, what are its constituents, and what is its be- 

 havior during cell-division ? Third, What is the structure of the 

 cytoplasm 1 Fourth, Are chromatophores present or not ? Fifth, 

 What kind of granules are present, and what is their position in 

 the cell, their structure, and their function 1 



The far-reaching importance of many of these questions, 

 which are still in controversy, and the writer's especial interest 

 in and familiarity with the group has led to the present cytolog- 

 ical investigation. 



