260 
METHODS IN PLANT HISTOLOGY 
For the development of sporangia use hot corrosive sublimate- 
acetic acid-alcohol, or chromo-acetic acid (1 g. chromic acid and 2c.c. 
acetic acid to 100 c.c. of water). A larger proportion of figures will 
be secured by adding 5 or 6 drops of 1 per cent osmic acid to this 
solution. Sections should not be more than 10 u in thickness and, 
for mitotic figures, 5 y is thick enough. 
Fig. 86. Osmunda cinnamomea: photomicrograph of sporangia with spore mother-cells 
in various stages of division; fixed in Flemming’s weaker solution and stained in iron-alum haema- 
toxylin; from a preparation by Dr. S. Yamanouchi. Negative by Miss Ethel Thomas. X114. 
For the reduction of chromosomes, the sections should not be 
thicker than 5 y. Osmunda is particularly good for this purpose be¬ 
cause the number of chromosomes is comparatively small. The 
young sporangia of Osmunda cinnamomea and 0 . Claytoniana show 
the mother-cell stage in the autumn, but the division into spores does 
not occur until the following spring, in the vicinity of Chicago, the 
mitotic figures being found during the latter part of April (Fig/86). 
O. regalis does not reach the mother-cell stage in the autumn. Mate¬ 
rial for mitosis should be collected during the first two weeks in May. 
