GYMNOSPERMS. IA$ 



nucleus toward the periphery of the cell (Fig. 57, D, c). With fur- 

 ther growth the generative cell with its nucleus becomes elliptical, their 

 major axis lying parallel with the longitudinal axis of the tube. The 

 two primordia of the blepharoplasts, which lay previously in line 

 parallel with the transverse axis of the tube, are now found in the ends 

 of the generative cell. About each there soon appear beautiful kino- 

 plasmic radiations, giving them a most striking resemblance to centre- 

 spheres with large centrosomes. Later in the period of development, 

 or about the middle of August in Japan, the young blepharoplasts 

 shift their position again, so that their earlier orientation in the gene- 

 rative cell with respect to the axis of the pollen tube is resumed (Fig. 

 57, E). The generative cell becomes spherical, and the kinoplasmic 

 radiations are very conspicuous. 



From this time until the end of September, or about one and one- 

 half months, few changes manifest themselves in the generative cell 

 apart from an increase in size. This period in the development is, 

 therefore, a period of growth, which corresponds to a similar period 

 in the development of the archegonium, and at the end of which all 

 elements have reached their maximum size (Fig. 57, E) . The diameter 

 of the generative cell, which contains dense cytoplasm, is about 0.14 

 mm., and that of the nucleus is about 60 /*. The primordia of the 

 blepharoplasts have also increased considerably in size ; they are about 

 15 (j.m diameter. Apart from the presence of one or more vacuoles, they 

 are rather homogeneous massive bodies. The kinoplasmic radiations 

 are still beautifully developed ; they seem to pass over gradually and 

 insensibly into the alveolar structure of the cytoplasm. 



About the middle of September the tube nucleus begins to migrate 

 toward the proximal end of the pollen tube, and, by the end of the 

 month, this nucleus, the generative, stalk, and outer prothallial cells 

 are all in the proximal end, which is capped by the exine of the spore. 

 It may be mentioned here that the migration of the tube nucleus into 

 the proximal end of the pollen tube seems to be a striking confirmation 

 of the doctrine of Haberlandt, namely, that in a growing cell the 

 nucleus generally takes a position near the seat of constructive activity. 

 Since the proximal end of the tube now grows toward the archegonium, 

 and as growth at the distal end ceases, it is to be expected, in harmony 

 with the theory of Haberlandt, that the nucleus which presides over 

 this growth should move toward the region of that activity. Webber 

 has observed the same behavior of the tube nucleus in Zamta. 



The final processes which now take place in the male gametophyte 

 have to do largely with the development of the two spermatozoids 



