DISK ALGAE 175 
247. Fertilization is effected by a sperm uniting with 
the egg in the oogone, usually by passing into the open 
end of the trichogyne. After fertilization the egg in- 
creases considerably in size, and forms a cellulose coat of 
its own. The cells which support the oogone send out 
lateral branches, which grow up and closely surround it, 
finally covering it entirely (excepting the trichogyne) 
with a cellular thick-walled “‘pericarp.’? The wholemass, 
including the fertilized oogone and its investing pericarp, 
constitutes the simplest form of spore-fruit (sporocarp). 
248. The further growth of the spore-fruit takes place 
the next spring by the swelling of the protoplasmic con- 
tents, and the consequent rupture of the pericarp; the 
inner portion divides into several cells (the proper fruit- 
spores), which give rise to zoospores closely resembling 
those developed from the vegetative cells. From each 
zoospore a new plant eventually arises. 
There is but one genus (Coleochaete) including a few 
widely distributed species. 
Laboratory Studies. (a) Scrape off a little of the green, 
paint-like coating from a flower-pot, a damp wall, or a side- 
walk plank, and examine under a high power for common 
Green Slime (Protococcus, etc.). 
(6) Gall-fungi may sometimes be found in Spirogyra and 
Desmids, and in the leaves of evening primroses, plantains, 
mints, and some leguminous plants. 
(c) Examine the green plants collected from ponds and 
ditches for Scenedesmus and Pediastrum. The former may 
often be found in great numbers on the glass sides of jars or 
aquaria. 
(d) In midsummer search quiet pools for Water Nets. With 
a fine scissors cut out a piece of one and mount carefully in 
water. Study with a low power of the microscope. Some of 
the coenocytes will be found producing zoospores. Search 
for young nets forming within the old coenocytes. 
(e) Collect fresh specimens of Sea Lettuce, put into a jar of 
