SPERMATOCYTES 



219 



beyond the groups previously considered in the loss of swimming 

 sperms and the related structures of the ovules, and also in other 

 features; nevertheless, it has also retained certain primitive features, 

 as, for example, the presence of mesarch bundles in the cotyledons and 

 even in the stem. The general relationships of the family will be con- 

 sidered in connection with the Pinaceae. 



(b) Pinaceae 



General character. — This family, characterized in general by its 

 conelike ovulate strobili and dry seeds, includes the conspicuous 



Fig. 485. — Transverse section of a three-year-old twig of Pinus sylvcstris, showing 

 the small pith, the thick and compact vascular cylinder of secondary wood, and the 

 cortex; radiating lines through the wood represent the narrow pith rays; resin ducts in 

 both wood (small) and cortex (large); to the right is a branch gap in the cylinder. 



gymnosperm vegetation of north temperate regions. Four tribes are 

 recognized, as follows: 



Abietineae (9 genera and about 140 species), including pines, spruces, 

 firs, hemlocks, larches, and cedars, the large genus being Pinus, with 

 about 80 species. 



