62 PROCEEDINGS OP THE AMERICAN ACADEMY 



contracted tissues to their lifelike appearance. Potassic hydrate 

 caused a general disintegration, and the various acids, unless used so 

 strong as to dissolve the whole mass, produced but little effect. For 

 this reason, the greater part of the work was done with sections cut 

 between pith, in sea-water, with a razor. Nothing else than sea- 

 water was allowed to touch them, and by this means sections were 

 obtamed that would keep alive three or four hours, after which time 

 they gradually contracted as they died. Almost all the drawings were 

 made from these fresh sections, and whatever work was done with 

 dried or alcoholic material was verified by means of them. Many 

 false appearances are given by the immense contraction which takes 

 place when the frond dies, and it was for this reason that these pre- 

 cautions were taken. In order to have a supply of fresh material con- 

 stantly on hand, I made excursions as often as possible during the 

 wmter to Nahant, where Choreocolax Polysiphoniai is fairly abundant. 

 The Choreocolax and the Polysiphonia on which it grew could with 

 care be kept for a considerable time, either in sea-water or moist in 

 a tin box. The latter way is perhaps the better, and if the box is 

 kept moderately cool, and has been well sterilized before putting 

 the material in it, the Choreocolax will keep alive from ten days to 

 two weeks. 



In conclusion, I wish to thank all those who have kindly helped me 

 in my work. To Professor W. G. Farlow I am especially obliged, 

 and to Dr. W. A. Setchell I am also indebted for several valuable 

 suggestions. 



Crtptogamic Laboratory, Harvard University, 

 March, 1891. 



