GYMNOSPERMS: WHITE PINE. 



209 



end of the ovule. This depression is thus known as the pollen 

 chamber. 



420. Now the open scales on the young female cone close up 

 again, so tightly that water from rains is excluded. What is also 

 very curious, the cones, which up to this 

 time have been standing erect, so that 

 the open scale could catch the pollen, 

 now turn so that they hang downward. 

 This more certainly excludes the rains, 

 since the overlapping of the scales forms 

 a shingled surface. Quantities of resin 

 are also formed in the scales, which 

 exudes and makes the cone practically 

 impervious to water. 



421. The female cone now slowly 

 grows during the summer and autumn, 

 increasing but little in size during this 

 time. During the winter it rests, that 

 is, ceases to grow. With the coming of 

 spring, growth commences again and 

 at an accelerated rate. The increase in 

 size is more rapid. The cone reaches 

 maturity in September. We thus see 

 that nearly eighteen months elapse from 

 the beginning of the female flower to the maturity of the 

 cone, and about fifteen months from the time that pollination 

 takes place. 



422. Female prothallium of the pine. — To study this we must make careful 

 longitudinal sections through the ovule (better made with the aid of a micro- 

 tome). Such a section is shown in fig. 269. The outer layer of tissue, which 

 at the upper end (point where the scale is attached to the axis of the cone) 

 stands free, is the ovular coat, or integument. Within this integument, near 

 the upper end, there is a cone-shaped mass of tissue, which farther down 

 continues along next the integument in a thinner strip. This mass of tissue 

 is the micellus., or the macrosporanghwi proper. The elliptical mass of tissue 

 within this, shown in fig. 271 is the female prothallium, or what is usually 

 here called the endosperm. The conical portion of the nucellus fits over the 



Fig. 268, 

 Macrosporangium of pine 

 (ovule), int, integument; w, nu- 

 cellus; Illy macrospore. (After 

 Hoffmeister.) 



