40 CLASS-BOOK OF BOTANY. 
ovule stage, the pollen tube, which fertilised it, entered by 
this opening. On removing the shell you will see that it is 
composed of two layers, the outer of which (the testa”) ig 
tough and thick, and the inner (or tegment) much thinner, 
Fig. 51. Seed of Bean, with testa removed, after germination has com- 
menced. (cot, cotyledons; pl, plumule; rad, radicle.) 
In the ovule these two coats are termed respectively the 
primine and the secundine. The embryo is composed of two 
thick cotyledons, rounded on their outer and flat on their 
inner surfaces. The radicle, or root-bud, is situated on their 
margin, with its point lying just under the micropyle, while 
between them, near the same margin, is the plumule,? or 
stem-bud, with its rudimentary leaves already showing signs of 
development. 
(7.) In the taller kinds of French Beans (Scarlet Runners, 
&c.) we see a mode of climbing different from any yet ex- 
amined. ‘These plants are twiners, and always twine in one 
direction only. In a seedling plant the first internode usually 
stands erect, but, owing to the rapid and unequal growth of 
the apex of the stem, the second and succeeding internodes 
curve to one side, and, as this curvature continually changes 
its position, the apex of the young stem moyes regularly round 
in a cirele or ellipse. If an upright support such as a stick 
be interposed at a little distance below the apex, the latter 
continues to moye round it, and in this way makes a series of 
revolutions on it, or, in other words, twines round it. In the 
French Bean, as in the majority of twining plants, the twming 
is from left to right—that is to say, that as you stand facing 
the plant the stem passes round the front of the support 
from your left to your right, and round the back from 
right to left. A few plants—e.g., the hop—twine in the 
opposite direction; but the noticeable feature is, that each 
plant has its specific direction, and no coercion will make 
it twine in a different. manner from that which is natural 
to it. . 
—————— 
* Tat. testa, a shell. 
| Lat. tegmen, a covering. 
t Lat. pluwmula, a little feather. 
