250 



APPLIED BIOLOGY 



( 244). Like fertilization in higher plants, this conjugation 

 mixes protoplasm from two individual Spirogyra plants, and 

 the mixture appears to have increased vitality (Fig. 77). 

 The physiology of such a one-celled green plant living in 

 water is briefly as follows : It absorbs water 

 and carbon dioxide, and these are used in 

 the making of starch or other carbohydrate 

 foods. From water also the plants absorb 

 the other elements necessary (N, S, P, K, 

 etc.) for making new protoplasm. These 

 elements are usually the same as in the 

 higher green plants. Also, the plant ab- 

 sorbs from the water the oxygen required 

 FIG 77 A conjuga- ^ or ^ e life-activities. The carbon dioxide 

 tion between cells produced by oxidation of cell-substances is 

 of two adjacent a b SO rbed by the surrounding water; but 



filaments of Spi- . . ' ' 



rogyra. Concen- during exposure to light is probably used 

 tration of proto- m ma king carbohydrates by photosynthe- 

 sis. Probably other excretions besides 

 carbon dioxide are formed in the one-celled 

 plants and absorbed by the surrounding 



progress in next water. 



240. Other green algae are numerous, 

 is beginning in low- They appear as greenish coatings on various 

 est pair of cells, objects in water, on the bottom of springs 



B, conjugation be- J . 



tween contiguous and ponds, and on pots and soil in green- 

 ceils of the same houses. Certain species are likely to grow 

 on the glass of aquaria. In such a position 

 it is easy to show their dependence upon light by shading 

 the glass with black paper in which openings (possibly in the 

 form of letters) have been cut. The alga3 will grow well 

 only where they receive the light. For descriptions of the 

 numerous forms which are of common occurrence, the student 

 must refer to textbooks specially devoted to the lower green 

 plants. 



plasm into one cell 

 of each pair, form- 

 ing a zygospore (z) , 



