CHLOROPHYCEAE 
189 
It is also found on stones and fences, and in moist situations generally. 
It is easily secured in nearly all localities and at all seasons. 
The life-history of Pleurococcus is variously described in textbooks, 
but it is very doubtful whether there is any mode of reproduction 
except by cell division. The zoospores and gametes which are some¬ 
times described probably belong to other forms which are occasionally 
associated with Pleurococcus, especially when growing in very moist 
situations. The life-history was ex¬ 
amined very critically by the great 
algologist, Wille, who not only con¬ 
cluded that cell division is the sole 
mode of reproduction, but showed how 
investigators, even those relying upon 
cultures, had made their mistakes. 
Wille’s paper was published in 1913 in 
Nyt Magazin for Naturvidenskaberne. 
A study of the living material is 
sufficient for any general course. The 
bright-green cells, scraped off and 
mounted in a drop of water, show the 
rather thick wall, the chromatophores, 
and usually the nucleus. A drop of 
iodine will bring out the nucleus, if it 
does not show already, and will also 
stain the pyrenoid, if the cell contains 
one. A mount in Venetian turpentine, 
stained in Magdala red and anilin blue, 
shows the nucleus very clearly. 
Vaucheria.—-This form can always 
be obtained in greenhouses, especially 
in the fernery, where it forms a green 
felt on the pots. The greenhouse 
form is likely to be Vaucheria sessilis. 
Another species, V. geminata, is very common in the spring, when it 
may be found in ponds and ditches (Fig. 42). Vaucheria is also found 
in running water, but in this situation is almost certain to be sterile. 
In the vicinity of Chicago, V. geminata appears late in March or 
early in April and within a few weeks begins to fruit abundantly. 
The fruiting continues for 4 to 8 weeks, and then the alga may 
Fig. 42.— Vaucheria: A, Vaucheria 
geminata, showing antheridium and five 
oogonia containing fertilized eggs; from a 
preparation fixed in formalin, acetic acid, 
and stained in iron-alum haematoxylin; 
B, V. sessilis ; from a preparation fixed 
in chromo-acetic acid and stained in eosin 
and gentian-violet. X150. 
