WATEE SILK SI 



ral conditions may be found by examining the 

 stigmas of various flowers with a hand-lens, espe- 

 cially lilies, hyacinths, fuchsias, etc., and having 

 found a stigma to which grains are attached, re- 

 moving them to the drop of syrup prepared as 

 above. 



Do you find variations in the time it takes 

 seemingly mature grains to germinate? Is the 

 pollen tube single or many celled ? 

 Make drawings to illustrate the different stages of 

 growth in pollen grains of the same kind and of differ- 

 ent kinds. 



Example 5.— Water Silk {Spirogyra Sp.) 



Material. — The study of this plant is introduced here 

 because its cells are so large and lend themselves so 

 readily to manipulation that they form most desirable 

 material for the study of the structure and functions of 

 the plant cell. 



These plants may be obtained in abundance during 

 the warm season of the year in almost any stagnant 

 pond or along the edges of slow-flowing streams. They 

 form the yellowish-green, frothy scum popularly called 

 "frog -spittle" or "pond -scum." Yarious species are 

 usually found growing together, along with other fresh- 

 water algae. Almost any species will serve for study, 

 but the larger kinds are especially favorable. They 

 may be kept for examination in winter in aquaria with 

 opaque sides, which should be placed in sunny windows, 

 be supplied with fresh water from time to time, and 

 kept partially covered to exclude the dust. In chang- 

 ing the water be careful to disturb the plant as little 

 as possible. If it be found that the water is becoming 

 infested with too many micro-organisms, transfer some 



