THE GREEN ALGAE OF NORTH AMERICA 89 



for microscopic, histological and cytological work is now so 

 elaborate and varied that no attempt can be made here to give 

 any details. Perhaps the best reference for it is Chamberlain's 

 Methods in Plant Histology. 



One process specially useful in studying herbarium specimens 

 of green algae appears not to be generally known or generally 

 mentioned in the technical works, and it may be well to note it 

 here. When a herbarium specimen of a green alga is mois- 

 tened and submitted to microscopic examination, it is often 

 found that the shape of the cell as well as of the chromatophore 

 has been lost in the shrinking in drying, and not recovered by 

 moistening. If then the bit of moistened alga is laid on the 

 slide, in a drop or two of concentrated lactic acid, then warmed 

 until bubbles appear in the fluid, it will often be found on put- 

 ting on the cover glass and examining the specimen, that the 

 structure of the original has been much restored. 



The instructions just given for collecting and preparing algae 

 are more in the way of hints and suggestions than of full direc- 

 tions. One learns by practice, and not much any other way ; 

 the "knack," the little contrivances, will soon be acquired. 

 Those who prefer fuller directions will find them in Harvey, 

 1852, Farlow, 1881, Setchell, 1899, Collins, 1899, West, 1904. 



Many kinds of algae can be kept alive for a long time, with 

 proper care as to fresh water, light etc.; development can be 

 studied, and often new and unexpected forms may appear; by 

 adding certain substances to the water, reproductive organs of 

 different kinds can often be developed ; but this, as well as the 

 matter of pure cultures, opens up too large a field for the 

 present work. 



As regards classification, a brief notice should be given. Any 

 statement, even approximately full, of the supposed phylogeny 

 and relations of the green algae would require more space than 

 can be given in a work of this character. The most plausible 

 theory now is that the green algae are descended from the 

 Flagellates, a class of organisms that has been claimed (and de- 

 clined) both by botanists and zoologists. The Flagellates are 

 actively moving unicellular organisms, and in nearly all the 

 green algae this ancestral form reappears as the zoospore, the 



