Introduction 9 



identifying them, they should always be carefully drawn to scale 

 with the help of a Camera Lucida. This is the surest way of 

 obtaining accurate measurements of the plants, and also much the 

 best way of impressing on the memory their diagnostic features. 

 Great attention should be paid by all students of Algse to their 

 cytological characters, the structure of the cell-wall, the disposi- 

 tion of the protoplasmic cell-contents, the form and structure of 

 the chromatophores, the presence or absence of pyrenoids, etc. It 

 is the absence of any definite information on these points that 

 renders many books on Algae almost useless. No student can 

 acquire erroneous ideas of such common genera as Ulothrix, Tri- 

 bonema (Conferva), Microspora, and others, if he has once realized 

 their fundamental cytological characters. 



CULTIVATION OF ALG^E. 



It is often desirable to cultivate Algse in order to investigate 

 their life-history and polymorphism. Under cultivation an Alga 

 is often under abnormal conditions, and as a result, it sometimes 

 develops strange forms which are quite unknown in the natural 

 state of the plant. Careful observation of these cultures frequently 

 affords good evidence towards the elucidation of the phylogenetic 

 relationships of Algse. Cultures can be made at various tempera- 

 tures, in water, in sugar solutions of various strengths, or if neces- 

 sary under damp conditions only. Cultures are most frequently 

 made in solutions of a nutritive character, but sometimes good 

 results are obtained in pure water or in weak saline solutions. A 

 medium containing gelose is very favourable for making pure 

 cultures of the lower Algse 1 . Klebs and others have emphasized 

 the usefulness of cultures on gelatine, agar-agar, and other solid 

 media, and cultivation experiments on damp porcelain plates are 

 frequently a success. The temperature necessary to obtain the 

 best cultures varies with different types of Algae, but 20 C. is a 

 good average temperature. 



1 Chodat and Grintzesco in Arch. Sci. Phys. et Nat. x, 1900, p. 386. 



