96 



MORPHOLOGY OP SPERM ATOPHYTES 



seems to have been the first to see all the four structures in the 

 pollen tube injected into the egg, an observation which has been 

 frequently confirmed since. It should be remembered, however, 

 that in the case of Taxus baccata Belajeff 30 reports the passing 

 into the egg of a single male cell only, the smaller one re- 

 maining in the tube. In Pinus, in Taxodium as sho\vn by 

 Ooker, 45 and in Cephalotaxus as shown by Arnoldi, 43 the upper 



part of the cytoplasm of the egg, 

 after the discharge of the tube, con- 

 tains two male cells, the disorgan- 

 izing tube nucleus and stalk cell nu- 

 cleus, besides cytoplasm of the tube 

 and starch grains. The cytoplasm of 

 the male cells is no longer distinguish- 

 able, and their nuclei may be recog- 

 nized by their large size and more 

 deeply staining contents as compared 

 with the tube and stalk cell nuclei, 

 which can hardly be distinguished 

 from each other. 



One male nucleus moves forward 

 through the cytoplasm of the egg, 

 the other three injected bodies re- 

 maining near the top of the egg and 

 gradually disappearing. Arnoldi 43 

 makes an interesting observation in connection with the func- 

 tionless male cell in Cephalotaxus Fortunei. He reports that as 

 it lies unused in the peripheral region of the cytoplasm of the 

 egg it may divide amitotically, one of his figures showing six 

 nuclei as having been derived from a single functionless male 

 nucleus. According to Blackman, 37 the functional male nu- 

 cleus moves very rapidly and increases in size, an increase appar- 

 ently due in some cases to actual increase of stainable substance, 

 and in others to vacuolation. The male nucleus of Pinus is 

 nearly spherical, with a diameter of about 40 /A, and is usually 

 one third (rarely one half) the diameter of the ellipsoidal or egg- 

 shaped nucleus of the egg. 



The behavior of the male nucleus after it reaches the egg nu- 

 cleus is peculiar (Fig. 74). According to Blackman, it pushes in 

 the membrane of the egg nucleus, and finally comes to lie within 



FIQ. 74. Pinus silvestris, the 

 male nucleus entering the 

 female nucleus (June 19th) . 

 x 135. After BLACKMAN. 



