468 BOTANICAL GAZETTE [December 



groups of chromosomes enter the same nuclear membrane, but 

 retain their former grouping; and (3) the chromosomes pair. The 

 first is illustrated by the paired nuclei in Uredineae; the second by 

 the chromatin groups during the first divisions of the Cyclops 

 embryo ; the third takes place soon after the fusion of the egg and 

 sperm in Abies. It seems altogether probable that the chromo- 

 somes do not actually pair until the prophase of the reduction 

 division in such animals as Cyclops. There is a striking similarity 

 between the pairing process as described in Abies and that con- 

 cerned with tetrad formation in some animals (compare diagram A 

 with diagram C). To what extent we are justified in suggesting 

 that the processes are identical and that they are both concerned 

 with the pairing of corresponding chromosomes from the egg and 

 from the sperm, only further research can definitely determine. 



Relationships 



Abies, as compared with Pinus, shows a number of primitive 

 characters : 



1. The male gametophyte : {a) an excessive polar ("prothallial") 

 tissue; (b) the equality of the male nuclei; both may function. 



2. The female gametophyte: (c) the large number of neck cells; 

 as many as five tiers (Miyaki 19) ; (d) the persistence of the ventral 

 canal cell; its nucleus may function as an egg nucleus. 



3. The ovulate strobilus and ovules: (e) the almost complete 

 separation of scale and bract ; (/) the development of a rudimentary 

 pollen chamber; (g) the comparatively free integuments. 



4. The staminate strobilus: (//) the staminate strobili are borne 

 on ordinary branches in the axes of ordinary leaves. 



5. The arrangement of leaves: (*) the spiral arrangement of 

 leaves on ordinary branches (Thomson 25; Lloyd 18). 



6. Vascular anatomy: (J) the general absence of ray tracheids 

 (Thompson 26, 27), which in Pinus are present in the mature wood, 

 but absent in the seedling and strobilus axis. 



It may be noted, however, that resin canals are not found in 

 the woody axis of the Abies stem except as traumatic responses 

 (Jeffrey ii). Jeffrey states that the presence of resin ducts is 

 an ancient character which has persisted in Pinus. "On account 



