CEDAR OIL — CHLORAL HYDRATE 291 



acid. Material which has been stained in bulk with carmalum 

 may be sectioned, and the sections may then be double-stained 

 with some aniline stain, such as blue de Lyon. See Borax- 

 carmine for another carmine stain. Very fine double staining 

 may be achieved by placing sections first in an aqueous solution 

 of iodine green and then for a somewhat longer time in carmalum. 

 By this treatment lignified membranes are stained by the iodine 

 green, while the unlignified membranes are stained by the 

 carmalum. , 



Cedar Oil. — Sections which are to be mounted in balsam 

 may first be examined in cedar oil to determine . their fitness 

 for permanent mounts; if they are satisfactory, the cedar oil 

 may be drained off and the balsam immediately added to the 

 sUde. Cedar oil has a clearing effect on sections which are 

 treated with it. 



Thicker cedar oil with a refractive index of about 1.515 is 

 used as an immersion fluid for homogeneous immersion lenses. 



Cedar oil is often used as an intermediary between alcohol 

 and paraffin in paraffin-imbedding, but for plant tissues chloro- 

 form is rather to be recommended. 



Chloral Carmine. — This is useful in clearing pollen grains 

 and staining their nuclei at the same time. It is prepared as 

 follows: Carmine 0.5 gm. and 30 drops of officinal hydrochloric 

 acid (specific gravity, 1.13 or 17° B.) are added to 30 c.c. of 

 alcohol, and this is heated for about thirty minutes on the 

 water-bath; then, after cooling, 25 gm. of chloral hydrate are 

 added, and the solution is filtered until clear. 



Chloral Hydrate. — Dissolve five parts of chloral hydrate 

 in two parts of water. The chloral hydrate may be taken in 

 grams and the water in cubic centimeters. This is one of the 

 best clearing agents. Whole leaves, when boiled in this solu- 

 tion, clear quickly to such an extent that they may be studied 

 by transmitted light throughout all of the cell-layers. Crys- 

 tals in leaves may be plainly demonstrated in this way. This 

 reagent is also very useful in clearing pollen grains, and em- 

 bryos within the ovules. 



