256 



Methods in Plant Histology 



In May, after the strobili break through the bud scales, material 

 is easily collected. Up to the time of pollination the entire ovulate 

 strobilus cuts easily in paraffin. Longitudinal sections of the cone at 

 this time give good views of the bract and ovuliferous scale bearing 

 the ovules. The integument is very well marked, and in the nucellus 

 one or more sporogenous cells can usually be distinguished. As soon 

 as the scales close up after pollination, the cone begins to harden and 

 soon makes trouble in cutting. Even before the scales close up, it 



. 



FIG. 88. Abies balsamea: photomicrograph of section of pollen grain about the 

 time of shedding; there are two prothallial cells, the stalk cell, body cell, and tube cell; 

 sometimes the division in the body cell also takes place before the pollen is shed; from 

 a negative by Mr. A. H. Hutchinson. X815. 



is better to cut a slab from opposite sides of the cone; after the scales 

 close, it is almost a necessity. For sections of the whole cone, fix 

 in formalin alcohol. Dr. Hannah Aase succeeded in cutting complete 

 series of paraffin sections from cones of Pinus Banksiana more than 

 2 cm. in length. She fixed them in formalin alcohol, and used pro- 

 longed periods in dehydrating, clearing, and infiltrating. Land's 

 bichromate of potash and glue fixative was used in fixing the sections 

 to the slide. Such series of sections of large cones were necessary for 

 an investigation of the vascular anatomy. 



