Lecture XX VII. 243 



Behind the root-cap the growing tip is made of cells which during 

 the active season are constantly dividing, and the cells so produced 

 add to the inner layers of the root-cap in front and to the cortex 

 and conducting strand behind. Soon after formation the vacuoles 

 of those cells, which have been added on to the cortex and con- 

 ducting tract, increase greatly in volume and the cells are 

 stretched to many times their original size. This growth adds 

 rapidly to the length of the root and pushes the apex on through 

 the soil, the exuviated outer layers of the root-cap lubricating its 

 way. 



The low conical stem of the bulb is composed largely of funda- 

 mental tissue formed of rounded cells filled with starch. Through 

 this pass the conducting tracts or vascular bundles coming from 

 the leaves. Their paths are irregular and they make frequent 

 connections with one another. In the lower parts of the stem 

 branches are given off from the conducting tracts to the roots. 

 The arrangement of tissues in the flowering stem is more orderly. 

 The mass of the stem is composed of fundamental tissue. Its 

 epidermis of elongated cells is covered with a cuticle. The cuticle 

 is perforated by numerous stomata and the stomata are each 

 bordered by two guard-cells. The arrangement of the guard-cells 

 towards one another is very; like that found in the Buttercup, but 

 the slits of the stomata are 'all parallel to the axis of the stem. 

 Below the epidermis is a layer of tissue formed of prismatic 

 elongated cells. The walls of these cells are specially thickened 

 at the angles so that in cross section the cavity of the cell appears 

 circular while the outline of the cell-wall is polygonal. Such tissue 

 is called collenchyma. It is usually found on the outside of erect 

 cylindrical organs, where the tissues are exposed to great stretching 

 forces. The cells of the collenchyma contain chloroplasts as do 

 the rounded thin-walled cells of the inner cortex inside them. The 

 central fundamental tissue is made up of short cylindrical cells with 

 rounded ends and they possess few chloroplasts but often contain 

 starch grains and other store materials. 



The conducting tracts from the bracts and flowers pass obliquely 

 downwards and inwards towards the axis as they enter the stem. 

 Before reaching the axis of this organ they turn sharply downwards 

 and then gradually turning outwards run down the stem. When 

 in their course they reach the inside of the cortex they run 

 vertically downwards and fuse with their fellows coming from 

 other bracts. During their downward path they pass round 

 the stem so that they follow a spiral course. This path of the 

 conducting tracts is very different from that which is found either 



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