282 
METHODS IN PLANT HISTOLOGY 
scales should be carefully removed so as to expose the delicate 
greenish cone within. At this time the sporogenous cells are easily 
distinguished. Material collected in January, or at any time before 
growth is resumed in the spring, shows about the same stage of 
development. If it is desired to secure a series of stages with the 
least possible delay, a branch bearing numerous clusters of cones 
may be brought into the laboratory and placed in a jar of water. 
Growth is more satisfactory in case of branches broken off in the 
Fig. 99. —Picea nigra: photomicrograph of transverse section of root. Fixed in alcohol and 
stained in safranin and Delafield’s haematoxylin. Eastman Commercial Ortho film, Wratten B 
filter (green); J. Swift and Son 1-inch objective; arc light; exposure, l second. Negative by 
Dr. P. J. Sedgwick. X28. 
winter than in those brought in before there has been any period of 
rest. The material can be examined from time to time, and a com¬ 
plete series is easily secured. The mitotic figures in the pollen 
mother-cells furnish exceptionally instructive preparations. The 
two mitoses take place during the last week in April and the first 
week in May. Staminate cones which will yield mitotic figures can 
be selected with certainty by examining the fresh material. Crush 
a microsporangium from the top of the cone and one from the bottom, 
add a small drop of water and a cover to each, and examine. If 
there are pollen tetrads at the bottom, but only undivided spore 
