234 METHODS IN PLANT HISTOLOGY 



tion of osmic acid (4 or 5 drops of 1 per cent osmic acid to 50 c.c. of 

 water) is good for zoospores and androspores. 



For cell division and the peculiar method of forming the new cell 

 wall, stain in phloxine and anilin blue. Iron-alum haematoxylin is 

 better for most of the other phases; but the fertilized eggs stain very 

 deeply. Consequently, stain some material lightly, for the fertilized 

 eggs; and some more deeply for young eggs, chromatophores, and 

 other phases. Mount in Venetian turpentine. 



For details of blepharoplasts and the development of the various 

 motile forms, material should be imbedded and sectioned. 



Nanandrous species have antheridia only in the dwarf males; and 

 species with antheridia in the ordinary filaments have no androspores 

 in the hfe-history. A species with no dwarf males in the life-history 

 (macandrous) is shown in Figure 56 A and B; a species with dwarf 

 males in the life-history (nanandrous) is shown in C of the same figure. 



In studying Oedogoniuvi diplandrum, Klebs found that a change 

 from a lower to a higher temperature would induce the production of 

 zoospores. A culture which had been kept in a cold room with a tem- 

 perature varying from 6° to 0° C, when brought into a warmer room 

 with a temperature varying from 12° to 16° C, produced an abundance 

 of zoospores within 2 days. Light does not seem to have any influence 

 upon the formation of zoospores in this species, but hght is necessary 

 for the formation of antheridia and oogonia. 



We have secured an abundance of oogonia and antheridia by keep- 

 ing the material for 4 or 5 days in a very weak Knop's solution and 

 then transferring to distilled water. The oogonia appeared in 3 or 4 

 days. The method seems to succeed with some species, especially those 

 which occur floating or suspended in the water, but we have not suc- 

 ceeded with species which form a fuzzy covering on grasses and twigs 

 under water. Sterile material sometimes fruits when brought into the 

 laboratory and placed in open jars with plenty of water and not too 

 much light. 



Co\eochsiete.— C oleochaete is epiphytic upon the stems and leaves 

 of submerged plants. Sagittaria is a good host plant. Look on petioles 

 from the surface of the water down to 6 inches below, where the alga 

 begins to get scarce. The well-lighted part of the host is better than 

 the shaded part. Three or four species may be found growing so close 

 together that they all come in the field of the microscope with a 16 mm. 

 objective. C oleochaete scutata is the best-known species, but C. soluta, 



