THE ALG^ 255 



and the thinness and fineness of division of the forms always 

 immersed, in adaptation to the difficulty of obtaining sufficient 

 oxygen, the toughness and elasticity and powerful holdfasts of 

 those dwelling between tide-marks exposed to the full force 

 of the waves, the bladders for floating, the red and brown 

 instead of green colors, probably in adaptation to the peculiar 

 light-conditions, all should receive attention. 



Exercise 74 is particularly valuable as calling attention to 

 the chief elements in adaptation. 



This study of Algae will occupy at least four, and better 

 six, two-hour periods. 



In this kind of study, I think collection is of great value. 

 The collecting instinct is one of the chief attributes of the 

 successful naturalist, especially of him who studies whole organ- 

 isms. The taking, the preparing, the keeping of specimens, 

 all have value in increasing acquaintance, and the reference 

 to them from time to time afterward is a pleasure and a 

 profit. But as most people lack this inclination, it is better 

 to make the collecting voluntary. Algae are easy to preserve. 

 Of Pleurococcus, a little may be scraped carefully off, put on 

 a small piece of paper, moistened, well spread out, and then 

 placed between driers, with a bit of cotton cloth over the 

 alga to keep it from sticking to the upper paper. Spirogyra 

 should be floated out well in water, then paper should be 

 slipped under it, and the whole lifted from the water, to be 

 dried afterward as in the Pleurococcus. These may then be 

 mounted in the book-herbarium described elsewhere (see page 

 no). A most valuable series may be made by mounting 

 specimens of all the plants studied in this Part II, and thus 

 would result a very instructive collection of types representing 

 the groups from Algae to Phanerogams. This would accord 

 with one division of the plan earlier recommended (page 104). 



