302 Phillips on a Comparative Study of the 



before it is affirmed as a fact. Macallum has shown that 

 its substance also contains "masked" iron. This view would 

 further lend color to its chromatin nature. What the func- 

 tion of the heterocyst may be, can only be a matter of con- 

 jecture at the present stage of our knowledge. The fact 

 that the heterocyst is usually next or near to the spores 

 might lead us to consider it as a storehouse of food for 

 them. The fact that when spores and heterocysts are in 

 connection, as in CyUndrospermum, they remain so long 

 after the trichome is broken up, would also appear to sub- 

 stantiate this view. 



(6) Spore Formation. 



One of the striking features of the Cyanophyceae is their 

 ability to withstand long periods of drought. Plants will 

 desiccate to such an extent that their size will not be more 

 than one-half of their original dimensions or about one- 

 eighth of their original bulk, and still if the proper environ- 

 ments be restored, the cells will revive and begin to vege- 

 tate and multiply. Such cells resume their activities in a 

 strikingly short period of time, and frequently with very 

 little moisture. In the rain-pools formed by the scanty rain- 

 fall on the deserts and semi-arid districts of the western part 

 of the United States a decided coating of Oscillaria will 

 frequently be formed within a few hours, all of which has 

 developed from such desiccated cells, which, during the so- 

 called rainy season, seem to be the principal means of tid- 

 ing the plant over the periods from one rainfall to the next. 

 These cells should not be termed spores, however, as their 

 cell contents do not undergo the changes apparently neces- 

 sary for the formation of a resting spore that will bridge 

 over long periods of drought. Such desiccated cells, when 

 collected by the writer in their native haunts, soon lost their 

 vitality, not even resisting a five weeks' trip eastward to the 

 laboratory, though it was easy enough to revive them three 



