236 METHODS IN PLANT HISTOLOGY 



preparations are very effective. All the species mentioned are flat: C. 

 pulvinata is hemispherical and might be mistaken for a small Rivularia. 



If you overstain with Delafield's haematoxylin and then reduce the 

 stain with hydrochloric acid (about 3 or 4 drops to 100 c.c. water), the 

 alga will stand out sharply against the host. A slight tinge of orange 

 in clove oil will increase the contrast. 



Sections are easily cut and, especially in forms with a flat thallus, 

 show features which might escape if one depended entirely upon 

 plants mounted whole. Cut out small pieces of leaf or stem abundantly 

 covered with Coleochaete, imbed in paraffin, and cut host and guest 

 together. 



Chara. — Chara is found in ponds, lagoons, and ditches. Once seen, 

 it is always readily recognized. In the ponds and lagoons along the 

 southern shores of Lake Michigan it fruits so abundantly that the 

 whole pond shows an orange color due to the immense numbers of 

 antheridia. In the lagoons of the Chicago parks Chara is so abundant 

 that it must be dredged out every summer. 



Chara is easily kept alive throughout the year in the laboratory. A 

 2-gallon glass jar with an inch of pond dirt, sand, and gravel at the 

 bottom, and nearly filled with tap water, is all that is needed for a 

 successful culture. If the jar is to be covered, it should not be more 

 than two-thirds full of water. Not more than a dozen plants should be 

 put into such a jar. 



A rather strong solution should be used for fixing. The following 

 will give good results : 



Chromic acid 1 g. 



Glacial acetic acid 1 c.c. 



Water 100 c.c. 



In about 24 hours this not only fixes but dissolves the lime with which 

 most species are coated. 



For paraffin sections select the tip of the plant, a piece about a 

 centimeter in length. Sections of this may show, not only the large 

 apical cell, but also various stages in the development of antheridia 

 and oogonia (Fig. 57). For the development of the plant body from 

 the apical cell and also for early stages in the development of oogonia 

 and antheridia, the safranin, gentian violet, orange combination is 

 excellent; for later stages, especially in the development of the an- 

 theridia, iron-haematoxylin is much better. 



The antheridium of Chara stains so rapidly that the beginner uni- 



