44 NEW ZEALAND NATURE-STUDY BOOK 
(5) There must be a sufficient and. suitable 
supply of food-material. This does not mean that 
there must be food-stuff available outside the growing plant 
or seed; that may be already in the plant or seed itself 
stored up in reserve. Ifa bean seed is germinated, taken 
up out of the ground, and carefully dried, so that all the 
absorbed moisture is got rid of, it (the seed itself) will be 
found not to have increased in weight. The food-material 
stored up in the seed has merely been transferred from one 
part of the plant to the other. 
Growth in Length. An interesting experiment to 
show what part of the root grows with most rapidity can 
be carried out as follows : 
Take a pea seed which has begun to grow, and mark on 
it with Indian ink a number of lines at equal distances 
apart. Suspend the seed in 
ajar over some water, The 
water will keep the air moist 
and so promote more rapid 
growth. If the plant be 
examined at the end of a | 
couple of days, it will be 
found that the distance be- 
Radicle tween the marks is practically 
when first the same except near the tip 
marked 
of the root. Here the con- 
secutive marks are now 
separated by a longer interval 
= <= _ showing that growth has been 
Fig. 37.—Pea-plant suspended in : 
jar over ene ee nOw te elongation most rapid at the apex of the 
Fees hea et root. Nearer the seed itself 
the radicle has hardly increased in length at all, 
The stem can be experimented on in a similar way. 
