164 



THE GROWTH OF ROOTS AND STEMS. 



surface, ultimately joining bundles from other leaves and 

 increasing in size, whereas in Monocotyledons the bundles 

 from each leaf run deep into the stem and curve outwards 

 lower down, tapering away as they do so. Hence the bundles 

 on the outside of a transverse section are in this case smaller 

 than the central ones, whereas in the Dicotyledon the smaller 

 bundles alternate with the larger ones (Figs. 55, 56). 



Fig. 55. Longitudinal 

 Course of the Bundles 

 in a Monocotyledonous 

 Stem. 



It is important to realise that the bundles in the stem 

 are continuous with the veins of the leaves on one hand and 

 with the veins in the vascular cylinder of the root on the other. 



(a) Soak the stem of a Broad Bean or Dead Nettle (try other 

 herbaceous Dicotyledons) for two days in dilute potash, and then for 

 two days in dilute nitric acid. Brush and scrape away the softer 

 parts, leaving a skeleton of the vascular tissue. Note the way in which 

 the bundles from the upper leaves join on to those of the lower leaves. 



(&) Another method of showing that the vascular bundles (veins) of 

 the leaf are continuous with those in the stem is to cut thick longitu- 

 dinal slices through the stem and the bases of the leaves, and place the 

 slices in caustic potash. 



