278 
METHODS IN PLANT HISTOLOGY 
shrinking if the pieces are not too large; but figures are not as satis¬ 
factory as in chromic material. 
For sections of the entire ovule, use safranin, gentian-violet, 
orange; for free nuclear stages in both gametophyte and sporophyte, 
Fig. 97 —Ginkgo biloba: photomicrograph of microspores at shedding stage, showing two 
prothallial cells, generative cell, and tube cell. Stained in iron-alum haematoxylin. Eastman Com¬ 
mercial Ortho film, Wratten B filter (green); Spencer 4-mm. objective, N.A. .66; ocular X6, 
arc light; exposure, 3f seconds. Negative by Dr. P. J. Sedgwick. X654. 
use iron-haematoxylin with a touch of orange; for the megaspore 
membrane, safranin seems to be the best stain. 
GYMNOSPERMS—CONIFERALES 
Since Pinus is an available laboratory type, we shall describe 
methods for demonstrating various phases in the life-history of this 
genus, hoping that the directions will enable the student to experi¬ 
ment intelligently with similar forms. The dates are for Pinus 
Laricio in the vicinity of Chicago, but dates will be different for differ- 
