ZYGOPHYTA. 119 
in certain specialized cells. These occupy particular por- 
tions of the plant-body, and compose the “fruit,” so called. 
In Devil’s Apron these fruits occur as bands or spots in 
the central part of the leaf. The union of zodspores to 
form a resting-spore (zygospore) has been observed in but 
few cases, and not at all in the larger and more commor 
species. 
Practical Studies.—(a) In midsummer search quiet pools for water- 
nets. With a fine scissors cut out a piece of one and mount care- 
fully in water. Study with a low power of the microscope. Some 
of the cells will be found producing zodspores. Search for young 
nets forming within the old cells. p 
(6) Collect a quantity of water-flannel, and put it in a large dish of 
water, leaving it over night. Next morning the side of the dish 
which is nearest the light will show a green band at the water’s edge, 
due to the myriads of zodspores which escaped during the night. 
Mount a drop of water and search for zodspores. Occasionally the 
escape of zodspores may be seen by mounting a number of filaments 
and searching carefully, 
(c) Collect sea-lettuce and study in the same way. 
(d) Study the tissues of Devil’s Apron (Laminaria) in cross and 
longitudinal sections. 
Crass II. Consueata. 
250. Here the sexual cells which unite are fixed; that 
is, they are not locomotive. The sexual act always takes 
place in the mature plant. No zodspores are produced. 
This class includes many plants of great beauty and scien- 
tific interest. Of the four orders here noticed the first 
three are composed of chlorophyll-bearing plants, while in 
the fourth they are destitute of chlorophyll. 
251. The Desmids (Desmidiacee) are minute unicellular 
fresh-water plants. The cells are of very various forms, 
usually more or less constricted in the middle, and divided 
into two symmetrical half-cells. The cell-wall is more or 
less firm, but never silicious. 
