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METHODS IN PLANT HISTOLOGY 



torn rounded like a test tube. The tube should be on top of the bath, 

 with the cork out, to evaporate as much of the xylol as possible. Put 

 it in the bath, standing it in some dish to keep it from tipping over. 

 As soon as the paraffin melts, draw it off with a pipette just a little 

 warmer than the paraffin. A hot pipette works well, but ruins the 

 material. Change the paraffin four times. Half an hour in the bath 

 should be enough for any of the Volvocales or any forms of similar 

 consistency. Imbed by pouring out into a small tray so that there 



Fig. 44. — Volvox: A, surface view of several cells, fixed in tiie hot aqueous corrosive sublimate- 

 acetic acid mixture, stained in iron-alum haematoxylin, and mounted in Venetian turpentine; B, 

 fixed in chromo-acetic acid, but otherwise treated like A ; C-G, fixed in 1 per cent chromo-acetic 

 acid, imbedded in paraffin, and cut 5^; C, E, and F stained in iron-alum haematoxylin; D and G 

 stained in safranin, gentian violet, orange; C, new colony showing pyrenoids, p, and nucleus, n; D,a, 

 nearly mature antheridium; E, young egg; F, egg before fertilization; G, egg after fertilization, 

 showing oil globules, o; pyrenoids, p; starch cut off from pyrenoid, s. All X780. 



shall be a layer of material about 2 mm. thick. If you have trouble in 

 pouring it out, just let it cool in the shell, putting it into luke-warm 

 water for 15 or 20 seconds, then into cold water. Break the shell. 

 There will be some loss of material in getting it ready for cutting. 

 Sections should not be thicker than 5 ju) 3 or 2 /x will be better for de- 

 tails. Safranin, gentian violet, orange, is a good combination for older 

 stages, especially for pyrenoids and starch. Iron-almii haematoxylin 

 is better for nuclei and the younger stages of oogonia, antheridia, and 

 new colonies. 



