1 62 Chapters in Modern Botany CHAP. 



First then in spring the bursting of the buds and the 

 unfolding of the leaves to the lengthening day ; then how 

 at the approach of winter, when the conditions of light, 

 heat, and moisture are no longer favourable, the leaves fall 

 off, and there is no obvious growth after they are gone. 

 Note too the many differences between the fresh growing 

 leaves and those which have withered and fallen off; for 

 one thing, the former are rich in starch and sugar, and other 

 substances which the dead leaves lack. In dying at any 

 rate the leaves surrender the best of their substance to the 

 permanent body of the plant. We shall see that they are 

 doing this all their life long. 



When voracious insects eat up all the leaves of a plant 

 and leave it bare, death often follows, although stem and 

 root are quite uninjured. And when a plant has received 

 some shock, as of frost or heat or poisonous smoke, or is 

 scarce of water, one of the first symptoms of ill-health 

 often a very rapid symptom is the drooping of the leaves, 

 so essential are they to the sustained life of the plant. 



Again, we are all familiar with the eatableness of many 

 leaves, such as those of cabbage, spinach, and lettuce ; they 

 are swollen out in great part with water, but also with 

 nutritive materials ; so we get an idea of the leaf as a part 

 of the plant in which substances are manufactured and 

 sometimes stored up. 



Experiments in Regard to Leaves. More precise 

 ideas about the uses of leaves may be gained by a few 

 simple experiments. Let us follow one of these described 

 by Detmer. 



Take some seeds, such as those of wheat, maize, and 

 beans ; weigh them, and let them germinate and grow in 

 water to which some plant ashes have been added. But in 

 order to get a more precise measurement of the amount of 

 material with which you begin, take samples of the seeds used. 



