ZTGOPHTTA. 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 zoospores to 

 form a resting-spore (zygospore) has been observed in but 

 few cases, and not at all in the larger and more common 

 species. 



PrcuMcal 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 zobspores. Search for young 

 nets forming within the old cells. 



(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 zoospores which escaped during the night. 

 Mount a drop of water and search for zoospores. Occasionally the 

 escape of zobspores 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 (Lamlnaria) in cross and 

 longitudinal sections. 



Class II. Conjxtgat^. 



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 zoospores 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 (Desmidiacece) 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. 



