16 BOTANY 
observe adaptation to surroundings. If the plant 18 
surrounded by other plants, or if it is grown with 
‘nsufficient illumination, the internodes will lengthen 
enormously in the endeavour to carry the leaves up to 
the light. This is well seen in a potato allowed to 
sprout in a dark cupboard or in a bag. | 
Note that, in the bean, the stem is square, though 
in most plants it is round. Such stem branches as are 
present are usually produced low down near the root, 
the higher nodes being occupied by flower-bearing 
shoots or inflorescences which after all, are only 
modifications of the former. Examine a number of 
other plants and observe that the stem branches arise 
in the axils of the leaves, 7.e., in the angle formed where 
the leaf-stalk meets the stem. 
Now make a horizontal cut, almost severing a piece 
of young stem. Pull the upper part downwards in 
such a way as to skin off some of the outer delicate 
coat from the lower. This skin is colourless, and 
protects the inner tissues. 
Next, completely sever the stem and note the thin 
green layer immediately inside the skin, and, beyond 
this, the ring of dark spots. The green tissue helps 
the leaves in their work, while the dark spots are 
really the cut ends of little strands of hard tissue that 
continue downwards to the root, and upwards to the 
leaf, where they branch into all the veins. Inside 
this ring is a layer of colourless tissue, and finally, in 
the middle, an open space. The bean stem then is 
hollow; but, by examining a number of other plants, 
it will be found that hollow stems are the exception 
rather than the rule. 
3. The Leaf (Fig. 1). Before examining the bean 
leaf, look at a few simple leaves in which the blade is 
all in one piece. Take for instance those of the poplar, 
the so-called garden nasturtium ( Tropeolum), the 
