214 METHODS IN PLANT HISTOLOGY 



for most of the washing; but finish the washing in fresh water and use 

 fresh water in making up alcohols and for the 10 per cent glycerin. 



For collecting, use "bolting cloth" or "bolting silk" of the finest 

 mesh available. With a piece of thin cloth about 15 cm. square, laid 

 over an ordinary coffee strainer, you can pour through about 4 hters 

 of water in a minute. In this way you will secure all the Volvox in 

 about a barrel of water in half an hour. Eudorina may be collected in 

 the same way. Smaller members of the Volvox family like Pandorina, 

 Gonium, and Chlamydomonas are too small to be held by the cloth; 

 but if material is very abundant, the water goes through faster than 

 the organisms and you will soon have many times as much material 

 in a bottle as you could get by dipping. Many small organisms are 

 effectively collected in this way, even when they are so small that most 

 of them pass through the cloth. 



Material of Volvox and all the Volvocaceae may be fixed in the cor- 

 rosive sublimate-acetic mixture, used hot — 85° C. If material is to be 

 stained and mounted whole, use the aqueous mixture; if it is to be im- 

 bedded and cut, use the alcoholic. For mounting whole, stain in iron- 

 alum haematoxylin, or in phloxine and aniUn blue, following the Vene- 

 tian turpentine method. 



Chlamydomonas is such an important type from the standpoint of 

 evolution and phylogeny, that there should always be a supply of liv- 

 ing material as well as some well-prepared slides. It often appears in 

 the greenhouse. A small quantity in a Petri dish on white sand, moist 

 but not flooded with water, may be kept for months. Add a pipette 

 full of water occasionally to keep it from drying up. If there are 

 zygotes, the material may dry up without any damage. If stained in 

 iron-alum haematoxylin, stain one lot heavily to show cilia; another 

 lot, lightly, to show internal structure. Some of each lot, with some in 

 phloxine and anilin blue, and some in iron-haematoxylin, on each 

 slide, make an instructive preparation. Of course, it is assumed that 

 there has been a thorough study of living material. The principal 

 stages in the life-history are shown in Figure 43. The Powers' methods 

 yield beautiful, transparent preparations. 



Volvox.— Volvox is found in ponds and ditches, and even in shal- 

 low puddles. The most favorable place to look for it is in the deeper 

 ponds, lagoons, and ditches which receive an abundance of rain water. 

 It has been claimed that where you find Lemna, you are likely to find 

 Volvox; and it is true that such water is favorable, but the shading is 



