I9IS ] HUTCHINSON— ABIES BALSAMEA 4^9 



of the reduced foliage of the abietineous conifers, this [that is, 

 resinous secretion] was a very serious drain on the assimilatory 

 apparatus. Gradually the more economical tendency arose of 

 forming resin passages in the case of need only." So regarded, 

 Pinus would be more primitive than Abies. Whether or not this 

 argument is sufficient to overbalance the numerous ancient charac- 

 ters of Abies previously tabulated is a matter of judgment which 

 we do not presume to decide. 



Many of the foregoing characters are such that they tend to 

 relate more closely the two ancient groups of Coniferales. the 

 Abietineae and the Araucarineae. 



Summary 



i. The male gametophytc— The polar (" prothallial ") cells may 

 divide mitotically. The body cell divides to form the male nuclei 

 while within the spore coat. Under favorable conditions a "pro- 

 thallial" cell may develop as an antheridial cell, a biantheridial 

 gametophyte resulting. The male nuclei are equivalent; one fuses 

 with the egg nucleus and frequently the other fuses with the ven- 

 tral canal cell nucleus. 



2. The ventral canal cell and ventral proembryo. — The ventral 

 canal cell nucleus breaks through its wall into the egg cytoplasm, 

 enlarges, and fuses with one of the male nuclei. A ventral pro- 

 embryo is formed by two successive divisions. 



3. The egg nucleus. — The egg nucleus enlarges to 60 times its 

 original volume. At the time of fertilization (fig. 28) irregular, 

 darkly staining, vacuolate masses, slender filaments pervaded by 

 small granules, spindle fibers, and chromatin are differentiated 

 within the nuclear membrane. The chromatin is the fundamental 

 nuclear substance; the other bodies are accretions gained during 

 the growth of the nucleus and excluded from the nuclei of the 

 proembryo. 



4. Fertilization and the first division. — After fusion two chroma- 

 tin groups appear at the base of the egg nucleus; in each 2X chro- 

 mosomes become separate; the two original spindles unite: the 

 chromosomes approximate to form * pairs ; they twist the one about 

 the other and become looped; each of the components of a pair 



