192 
METHODS IN PLANT HISTOLOGY 
material is largely vegetative. Another species is found in stagnant 
ponds, ditches, and even in watering-troughs and rain-barrels. It is 
difficult to keep in the laboratory the forms which are found in rapidly 
flowing water. However, if they are brought in still attached to 
stones and placed under a stream of tap water, they may live for a 
couple of weeks and may produce zoospores every morning. The 
production of zoospores may continue for a few days, if the material 
is merely put into a jar of water; in a 2 to 4 per cent cane-sugar 
'solution the production of zoospores continues a little longer. 
No form is better than Ulothrix for illustrating to a class the 
difference between zoospores and gametes. Even when gametes 
are not conjugating, their more rapid movement is noticeable; 
and when conjugating, the awkward, jerky movements of the pair 
contrasts sharply with the graceful movements of the zoospores. 
Fix in the special chromo-acetic-osmic solution and stain some 
material in iron-alum haematoxylin, which will differentiate the nuclei 
and pyrenoids; and stain some in Magdala red and anilin blue, 
which is better for the cell wall and chromatophore. Mount on 
each slide material from both lots, and the preparation will then 
afford a rather complete study. 
Oedogonium.—Most species are found in quiet waters, especially 
in ponds and ditches. The best fruiting material is often attached to 
submerged twigs, rushes, and various plants, where, to the naked eye, 
it forms only a fuzzy covering. Some species form floating masses, 
bearing some resemblance to Spirogyra, but they are not so slippery. 
The special chromo-acetic-osmic solution is good for the filaments; 
the iodine solution used in testing for starch, or a weak aqueous 
solution of osmic acid (4 or 5 drops to 50 c.c. of water) is good for 
zoospores and androspores. 
For cell division and the peculiar method of forming the new cell 
wall, stain in Magdala red and anilin blue. Iron-alum haematoxylin 
is better for most of the other phases; but the fertilized eggs stain 
very deeply. Consequently, stain some material lightly, for the 
fertilized eggs; and some more deeply for young eggs, chromatophores, 
and other phases. Mount in Venetian turpentine. 
For details of blepharoplasts and the development of the various 
motile forms, material should be imbedded and sectioned. 
Nanandrous species have antheridia only in the dwarf males; 
and species with antheridia in the ordinary filaments have no andro- 
