The Inner Structure of the Plantlet. 49 
67. The Growing Point. At the tip of the stem, and 
just behind the tip of the root, is a group of cells forming 
the so-called growing point. These cells divide very rapidly 
during the growing season, and from them, all other kinds 
of cells are evolved. 
68. The Vascular (vas’-cu-lar) Bundles.* While the 
plantlet remains within the seed-case, it mainly consists of 
cells more or less cubical or globular in outline. But 
scarcely does germination commence before some of the cells 
begin to increase greatly in length without a corresponding 
increase in thickness.t These elongated cells form in 
groups or bundles (vascular bundles) 
that extend lengthwise through the 
stem and roots, and since the individual 
i 
cells overlap each other and are in inti- 
= 
mate contact, they form threads or 
see 
ei 
fibres. These fibres serve the double 
purpose of giving strength to the plant, 
and conducting water, with its dissolved 
food materials, to the different parts. 
By the absorption of the ends of some 
of the cells, tubes (ducts) of very con- 
siderable length are formed. In other 
cells of vascular bundles, the walls are 
Fre 18. Prosenchyma mych thickened and strengthened by 
cells from stem of rye. 
Highly magnified. (After WOOdy deposits. These groups or bund- 
Frank and Tschirch). —_ Jes of fibres and ducts divide and sub- 
divide, in the leaves, forming the so-called veins and vein- 
* Also ealled fibro-vascular bundles. 
+ Cells of the former class are called Parenchyma (pa-ren’-chy-ma), and those 
of the latter class prosenchyma (pro-sen’-chy-ma). Fig. 18 shows prosenchyma 
cells from the stem of rye. Fig. 15 shows parenchyma cells from the apple leaf. 
