ACROGENS. 115 



and scalariform, or ladder-like) and fibrous or woody 

 tissue, forming together the sclerenchyma, or harder tis- 

 sues. (Chap. IV, Sees. 6 to 10.) 



In Fig. 45 the acrogenous growth of a fern is illus- 

 trated, together with the metamorphosis of the terminal 



FIG. 45. Diagram, showing the mode of growth in the stem of a Fern. A. B. C. 

 Stems of ferns showing successive stages of growth, a. a. a. Terminal cells, the latter 

 just after being produced by division, b. A cell which will give rise to an internode. 

 c. Shows a ring or cluster of cells giving rise to a node. d. Epidermal cells, e. Parenchyma. 

 /". Sclerenchyma. g. Scalariform vessels, h- Spiral vessels, k. An appendage, originating 

 at the node. d. e.f. g. and h. all arise from the multiplication and metamorphosis of the 

 "growing" cells. 



cell into the various tissues. In flowering plants the 

 terminal cell of the leaf-bud becomes barren, and the 

 enlargement of the leaf depends on the multiplica- 

 tion and growth of cells nearer the base ; but in the 

 fern the leaf-bud grows as the stem does, so that the 

 peduncle is first formed, then the embryo leaf, then the 

 pinnules, etc. 



Underneath the frond of a fern we may sometimes see 

 little brown patches. Each patch is a sorus, (sometimes 

 covered by a membrane called an indusium^] and the 

 little brown bodies constituting it are sporangia, or 

 spore-cases, which have been developed from epidermal 

 cells. An elastic ring (annulus) surrounds each sporan- 

 gium, and assists in opening it. The growth of these 



