CONIFERALES (PINACEAE) 



287 



during fertilization in the various species of pines which have been 

 studied. In Tsuga it is stated that the two sets of chromosomes are 

 associated, but remain distinct in the equatorial region of the first 

 spindle. In Juniperus, while there are slight differences in details, 

 the essential features are quite similar. Whether this independence 





338 339 



Figs. 338-340. — Fertilization in Juniperus communis: fig. 338, chromatin of 

 sperm and egg nuclei in late prophase within the limits of the egg nucleus; fig. 339, 

 later stage in which the egg and sperm chromosomes are no longer distinguishable; 

 fig. 340, first division of fertilized egg; XS20. — After Noren (132). 



of male and female chromatin continues into succeeding cell genera- 

 tions or not is a most important question. In his investigation of 

 Sequoia sempervirens, however, Lawson (92) concluded that in fusion 

 the two chromatic masses form a common network, in which the male 

 and female constituents become indistinguishable. 



4. The embryo 



The development of the embryo, as in the preceding groups, 

 includes two general stages: (i) the development of the proembryo, 

 which is the preliminary tissue developed in the base of the egg; and 

 (2) the growth of the suspensor into the endosperm and the develop- 

 ment of the embryo proper at its tip. Among Pinaceae the proembryo 

 is a much less extensive tissue than among Cycadales and Ginkgoales, 

 being a few cells at the base of the egg, the bulk of the egg functioning 



