APPENDIX. 185 



the object for some hours in it. It may then be imbedded as fol- 

 lows : Dip the smaller end of a tapering cork in the celloidin solu- 

 tion, allow it to dry for a moment (blowing on it if necessary), and 

 then build upon it a mass of celloidin, allowing it to dry a moment 

 after each addition. Transfer the object to the cork and cover it 

 thoroughly with the celloidin. Then float the cork in 82-85$ 

 (0.842 sp. gr.) alcohol until the mass has a firm consistency (24 h.). 

 It may then be cut in the microtome with the oblique knife, which 

 must be kept dripping with 82-85$ alcohol. Keep the sections in 

 82-85$ alcohol until ready to mount them, then soak them for a 

 minute in strong alcohol, transfer to a slide, pour on chloroform 

 until the alcohol is removed, drain off the liquid, quickly add a 

 drop of balsam, and cover. (See also Whitman, 1. c., p. 113.) 



OBJECTS FOR STUDY. 



Most of the plants and animals used in the practical studies can 

 be readily procured nearly everywhere, either in the field, in the 

 market, or in hot-houses. We have usually been able to obtain 

 them at reasonable prices from Mr. Win. P. Seal, 205 South Elev- 

 enth Street, Philadelphia. 



Anacharis, Chara, Nitella, Vallisneria, and Spirogym (green 

 pond-scum) occur in ponds or slowly running streams. Trades- 

 can fia is common in gardens and hot-houses, and any of the culti- 

 vated species will answer. Vaiiclieria commonly forms dense green 

 mats on the surface of flower-pots in hot-houses ; the larger species 

 are aquatic, and are often associated with Spirogyra. Amceba may 

 usually be found in the ooze at the bottom of bog-pools, particu- 

 larly in Sphagnum-Bwamps. Gregarina may often be procured by 

 stripping earthworms through the fingers, puncturing the swollen 

 end, and examining the fluid which issues. 



Pteris aquilina may be obtained in good condition between June 

 and September. For demonstrating the general features and the 

 coarser anatomy entire plants should be preserved in 50$ alcohol, 

 though dried specimens answer fairly well after being soaked some 

 time in water. For histological purposes the terminal buds, parts 

 of the leaf, and pieces of the rhizome from 1-3 inches long should 

 be kept on hand preserved in 70$ alcohol, to which they may be 

 transferred after preliminary treatment for a few days with 50$ 

 alcohol changed every day or two. For fresh material in winter 

 any of the hot-house forms of Pteris will answer, so far as the 

 structure of the leaf and reproductive organs is concerned, but 



