THE GROWTH OF ROOTS AND STEMS. 161 



and observe the vessels in the central cylinder ; some vessels have a 

 spiral fibre coiled inside them, others show small spots (pits), which 

 are thin places in the wall. Notice also the large cells of the rind 

 (cortex). Try to find the beginnings of side-roots and different stages 

 in their growth. 



193. The Conducting Channels of the Stem. From 

 your study of the functions of the leaf you should be able to 

 draw some conclusions regarding those of the stem. Some 

 further experiments will give additional information about 

 the part played by the stem in the process of transpiration. 



* (a) Place whole plants, or seedlings, or cut twigs, into water 

 coloured with red ink, set them where the conditions are favourable 

 for transpiration, and after an hour or so cut across the root and stem 

 at various points. If the coloured water has risen in the stem, trace it 

 upwards by means of successive cuts, then replace the plant in the 

 liquid, and after a time notice its appearance in the leaves, as shown 

 by the colouring of the veins. Note that in the root the stained veins 

 are at the centre. 



(6) Make thin cross-sections and longitudinal sections of these 

 plants. In most cases notice that the bundles are arranged in a single 

 ring ; this arrangement is found in most Dicotyledons. In Grasses, 

 Lilies, and other Monocotyledons the red-stained bundles will be seen 

 to be scattered through the stem. Notice that in most cases only 

 the inner part of each bundle is stained. In Vegetable Marrow or 

 Cucumber the bundles are in a double ring, and here the central part 

 of each bundle is stained. 



(c) Place a twig of a tree e.g. Oak, Beech, Elm, or any other hard 

 woody plant in the coloured water, and when the leaf- veins become 

 coloured cut across the stem, starting in this case at the top where the 

 stem is soft and green. At the top notice that the bundles are separate ; 

 but as we pass downwards, making successive cuts, the bundles appear 

 to fuse and form a continuous ring. 



(d) Cut two twigs of a woody plant e.g. Willow about equal as 

 regards length and the number of leaves. Cut round one of the twigs, 

 a few inches from the lower end, as far in as the hard woody part, 

 and remove from the lower part of the stem the whole of the soft outer 

 tissue. Leave the other twig uninjured, and set both twigs into red 

 ink. Notice that the removal of the outer tissue makes little or no 

 difference as regards the rise of the red ink in the stem and its appear- 

 ance in the veins of the leaves. 



The foregoing experiments show (1) that one function of 

 the stem is to carry water from the roots to the upper parts 

 of the plant, and (2) that the water travels through the 



S. B. 11 



