ISTichols, A morphological study of Juniperus communis var. depressa. 229 



living egg nucleus in Dioon, writes that his results are far from 

 satisfactory, that "anucleolus is visible, but otherwise the contents 

 are nearly homogeneous. There are few globules and the network 

 could not be identified". He adds: "It is possible that most 

 of the globules and the network are coagulation products due to 

 fixing". 



Maturation of the egg nucleus. — The egg nucleus 

 grows rapidly, usually becoming slightly ovoid in shape, and shortly 

 before fertilization has acquired a length of about 40 jli. Figs. 86 

 and 87 show two of the various aspects which it presents during 

 its development, while %. 92 represents the mature oosphere 

 nucleus. At the time of fertilization the reticulum appears as a 

 network of almost colorless, granulär threads which ramify through- 

 out the nucleus and exhibit slight indications of a differentiation 

 into chroniatin and linin, while sometimes there is also visible in 

 the nuclear cavity a faint protoplasmic meshwork (flg. 87). Coin- 

 cident with the growth of the egg nucleus the vacuole of the egg 

 cell diminishes in size (figs. 91, 95). 



Fertilization. — Fertilization stages were found in material 

 collected June 15 th , 1906 and June 29 th , 1907. In 1908 daily 

 collections from June 6 th to 13 th showed that, although fusion is 

 almost simultaneous in all the archegonia of a Single ovule, a week 

 or more may elapse between conjugation in different flowers on 

 the same plant. In material collected June 7 th , for example, the 

 body cell in many pollen tubes had not yet divided, while in 

 other cases fertilization had taken place and the development of 

 the proembryo had begun. 



Preparatory to fertilization the membrane of the pollen tube 

 is dissolved or ruptured directly above the neck of an archegonium, 

 and one of the male cells squeezes through the neck into the egg, 

 carrying the broken-down neck cells with it. There is no receptive 

 vacuole in the oosphere, such as occurs in the Äbieteae. The 

 wall of the male cell is cast off during its entrance into the egg, 

 or immediately afterward, and is frequently seen lying either out- 

 side the neck or, together with the disorganized remains of the 

 neck cells and vegetative nuclei of the male gametophyte, in the 

 upper part of the egg. Reference has already been made to the 

 equality in the size of the male cells, and ample proof has been 

 found that both may be functional. Numerous cases were noted 

 where the number of developing proembryos is greater than that 

 of the pollen tubes present, while fig. 95 shows one instance where 

 two male cells from the same pollen tube (the only pollen tube 

 present in this ovule) are in the act of entering different arche- 

 gonia. In the event of more than one male cell entering the 

 same archegonium only one functions, the superfluous cell disinte- 

 grating in the upper part of the egg cell. 



The male nucleus, accompanied or followed by its mantle of 

 cytoplasm and starch, rapidly approaches the female nucleus which 

 has come to lie slightly above the center of the egg. Figs. 

 96 — 101 illustrate the general appearance of the conjugating nuclei, 



