86 THE STORY OF “PLANT ‘Live 
roots are possessed of tubercles. These are really 
lateral buds transformed into tubercles, which are 
the home of certain bacteria that possess the power 
of storing up nitrogen, derived from the atmosphere. 
In some way the plant derives not only nourishing 
substances from the bacteria, but actually when they 
have absorbed a sufficient amount of nitrogen in the 
root-cells, absorbs these organisms also into its 
rapidly built-up tissue. Besides being so rich in 
nitrogenous matter leguminous plants also enrich 
poor ground, and serve as a forerunner for such 
exhausting crops as wheat. When used also as 
manure they have the same energising effect. 
In most cases the stem of the plant is erect and 
leafy, though many of these, e.g. Vetches, are climbing 
plants, climbing by the leaf tendrils. In the Gorse 
there are needle-like spines or modified leaves. 
The leaves are alternate, with stipules below, com- 
pound, often pinnate. At night the leaves may go to 
sleep and close up as in Clover. The Sensitive Plant 
or Mimosa is a classic example. 
The flowers are in racemes, panicles or spikes, and 
are regular and polygamous, or irregular and herma- 
phrodite. The receptacle is convex or flat and the 
flower is perigynous. The calyx develops in ascending 
order, and is made up of five sepals, the odd or oldest 
being anterior, and united. The corolla is made up 
of five petals, a standard, two ale, and a carina made 
up of two conjoined. The stamens are ten, united. 
or free ; when forming a tube one (the tenth) is free. 
