SPERMATOPHYTES— GYMNOSPERMS 



325 



together with a string, letting about a centimeter project beyond the 



string. Dip the whole thing in paraffin 2 or 3 times. There will be no 



infiltration, but the paraffin will hold the leaflets in place. Cut on a 



sliding microtome with an oblique stroke, placing the sections in a dish 



of cold water as fast as they are 



cut. The sections fall out from the 



paraffin, which is easily skimmed 



away. Fix the sections in formalin 



acetic alcohol for 24 hours; harden 



in 85 per cent alcohol, 24 hours; 70 



and 50 per cent alcohol, 1 hour each. 



Stain in safranin and light green. 



Don't make the periods too short, if 



you want the best preparations. 



Spermatogenesis. — Except in the 

 earliest stages, the staminate cones 

 are too large to be cut whole. The 

 individual sporophylls, with their 

 sporangia, cut easily up to the 

 formation of microspores; then the 

 sporangium wall hardens rapidly 

 and cutting becomes difficult. Up to 

 the young microspore stage, fix in 

 chromo-acetic-osmic-acid solution 

 (1 g. chromic acid, 2c.c. acetic acid, 

 6 c.c. 1 per cent osmic acid to 100 

 c.c. water). With a larger propor- 

 tion of acetic acid, our results have 

 not been satisfactory. 



Up to the stage when the micro- 

 spores become free, stain in iron- 

 alum haematoxylin. As soon as 

 the microspore mother-cells become 



free, the Belhng method, as modified by Dr. McClintock, can be used. 

 Try this: Squeeze the microspore mother-cells out into a thin smear, on 

 a slide with a very thin coat of Mayer's albumen fixative. Invert for 

 2-5 seconds over the mouth of a bottle containing 1 per cent osmic 

 acid. Put on very gently with a pipette a couple of drops formalin 

 acetic alcohol (formalin 1 c.c, acetic acid 1 c.c, absolute alcohol 



Fig. 111. — Encephalartos altensteinii: part 

 of transverse section of root, showing cambi- 

 um, with 3 rows of xylem cells below, and 

 phloem above; the latter with several thick- 

 walled suberized cells. X 230. 



