74: EASY LESSONS IN VEGETABLE BIOLOGY. 



CHAPTER XL 



EXOGENS, OR OUTSIDE GROWERS. 



1. PLANTS which produce woody and vascular layers 

 near the circumference of the stem are very numer- 

 ous, including about 70,000 different species. 



Between the woody layers, or rings, and the bark 

 of such plants is a semi-fluid mucilaginous matter 

 containing the new or growing cells. This layer is 

 called the cambium layer. At the apex of the 

 stem, and at that of the root, this layer is continuous 



with the cells of bioplasm 

 which multiply by self-di- 

 vision in these localities so 

 as to supply the elements of 

 the new tissues. (Fig. 33.) 

 2. Incomplete Exog 'en sare 

 those whose flowers have no 

 corolla. Sometimes, but not 

 always, they have a calyx, 

 or simple perianth. They 

 are of two kinds : 1) Those 

 whose seeds are naked, as 

 Fig. 33. in the Cone-~bearing family, 



consisting of the Fir and Spruce tribe, the Cypress 



