170 



Methods in Plant Histology 



abundance of zoospores within two days. Light does not seem to 

 have any influence upon the formation of zoospores in this species, 

 but light is necessary for the formation of antheridia and oogonia. 

 Any culture solutions must be very weak. Sterile material sometimes 

 fruits when brought into the laboratory and placed in open jars with 

 plenty of water and not too much light. 



Fix in chromo-acetic acid and use the Venetian turpentine 

 method. Iron-haematoxylin is good for antheridia and also for 



nuclei and pyrenoids, but anilin blue is better for 

 caps and cell walls and for some of the cell con- 

 tents. It is better to stain material in both ways 

 and then put some from each lot on every slide 

 (Fig. 35). 



Coleochaete. Coleochaete is epiphytic upon 

 the stems and leaves of submerged plants. C. 

 scutata, which is the most common species, has a 

 flat, orbicular thallus generally less than 1 mm. 

 in diameter. C. pulvinata has a hemispherical 

 thallus and might be mistaken for Rivularia, un- 

 less examined with a lens. 



For most purposes it is better to mount the 

 whole plant. Complete the staining before trying 

 FIG. 35. oedogo- to remove the Coleochaete from its host. Dela- 

 m: egg shortly field > g haematoxylin is a good stain. Test the 



after fertilization, 



showing nucleus, staining by removing single specimens and examin- 

 moSriai. 8 ' X465 ( m S them under the microscope. When the stain- 

 ing is satisfactory, wash thoroughly in water and 

 transfer to 10 per cent glycerin and follow the Venetian turpen- 

 tine method. When the turpentine is thick enough for mounting, 

 remove the plants from the stem or leaf and make the preparations. 

 The plants may be removed before fixing or at any stage in the 

 process, but they are so small that great care must be taken not to 

 lose them when changing solutions. 



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 



