Hazen: Lire History oF SPHAERELLA LACUSTRIS 233 
pose both in the greener and in the pure red cells. In the case of 
the red cells of Sphacrella nivalis* especially it appears that such a 
function would be of great value, since the heat created would be 
available in melting the snow. Moreover, I have been struck with 
the fact that, in cultures kept under precisely the same conditions 
in the laboratory, material from milder climates, e. g. from New 
York ‘and Baltimore, habitually develops more chlorophyl than 
material collected in places which are frozen a large part of the 
winter, as at Burlington, Vermont, and Plattsburgh, New York. 
From the fact that the haematochrom is wrapped about the 
nucleus, and except in rare cases (Fig. 33) envelops each daughter- 
nucleus during the process of division, it might be nate that it 
has some food value. 
The key to its most important function, however, may lie in 
. the chemical nature of the haematochrom. It possesses much 
greater stability than chlorophyl and therefore probably plays an 
important part in enabling the cells to endure adverse circumstances. 
I have found that zooids furnished with considerable haematochrom 
are less quickly destroyed by sudden changes of light and tem- 
perature than greener ones. 
IRRITABILITY OF ZOOIDS 
The zooids of Sphaerella furnish very interesting material for 
studies in sensitiveness. In general they are strongly attracted 
toward light so that, when they are cultivated in glass vessels, the 
margin of the water nearest the light will be colored red or green 
by the accumulation of zooids in that part, while very few will be 
found in other parts of the vessel. 
This light-seeking tendency, however, varies somewhat with 
circumstances. Strasburger (’78) found that the young zooids 
would swim towards a light from which they would move away 
when older, and that though zooids sought the light at a tem- 
perature of 16?—18^, they shunned light of the same intensity at 
4°. Ihave found, on the contrary, that when reduced gradually 
* Dr, J. G. Hunt (Am. Nat. 9: 575. 1875) states that the coloring matter of 
‘red snow’’ leaves unchanged the red, orange and yellow portions of the spectrum 
but entirely absorbs the violet portion. It may be assumed, then, that the coloring- 
matter of Sphaerella nivalis is identical with "d haematochrom of S. Jacustris. 
