LEAVES AND ROOTS— THEIR FUNCTIONS AND STRUCTURE. 



317 



Relative to the nitrogen of plants, Prof. 

 LiEBiG states — " Plants, and consequently 

 animals, must therefore derive their nitro- 

 gen from the atmosphere." And again, he 

 says — "Nitrogen is found in lichens which 

 grow on basaltic rocks. Our fields produce 

 more of it than we have given them as 

 manure ; and it exists in all kinds of soils 

 and minerals which were never in contact 

 with organic substances. The nitrogen in 

 these cases could only have been extracted 

 from the atmosphere." " No conclusion 

 can, then, have a better foundation than 

 this, that it is the ammonia of the atmos- 

 phere which furnishes nitrogen to plants." 



I have already said, that the stomata of 

 the leaves, as it were, iiihale the carbonic 

 acid gas of the atmosphere, where it un- 

 dergoes decomposition, retaining the car- 

 bon, and, as it were, exhalmg the oxygen. 

 This, by the older physiologists, was com- 

 pared to the breathing of animals. Hence, 

 the leaves were termed the lungs of plants, 

 the organs of breathing, or of respiration. 



Let us now turn our attention to the 

 roots of plants. The true roots of plants 

 are the radiculae, or fimbriee, — the rootlets, 

 striking out at all points from the stem and 

 branches which lie under the earth. It is 

 necessary to understand the organization 

 of the rootlets, — in my opinion, very im- 

 portant organs to the proper growth of 

 plants. If we make a longitudinal section 

 of the rootlet, to the point where it is 

 given off from the root, and continue the 

 section through the branch of the root, (the 

 most simple and easy of demonstrations is 

 the carrot,) we shall see, that while the 

 outer coat of the rootlet is given off from 

 the external coat of the root, there is a ves- 

 sel running from the extreme point, or 

 8po7igiole, along the center of the rootlet, 

 continuing its course entirely through the 

 bark, until it meets the ascending vessels. 



through which the sap arises into the plant. 

 The root appears to act to the maturer {)lant, 

 in some measure, and in a similar manner, 

 as the seed-lobes, or cotyledons, to the young 

 plant. The seed-lobes, you are aware, con- 

 tain an immensity of vegetable matter of 

 the nature of starch, which, being con- 

 verted into dextrine by the peculiar chemi- 

 cal change, effected in the process of ger- 

 mination and vegetation, by the diastase 

 contained in the germ, and serves for the 

 nourishment of the young plant imtil its 

 organs are so developed as to procure its 

 food elsewhere. 



I have made use of the term diastase. 

 As that word is not yet in common use, it 

 may be well for me briefly to explain it. 

 Diastase is a peculiar nitrogenised com- 

 pound, contained in the. germ of seeds, 

 which, upon the application of heat, mois- 

 ture, and atmospheric air, commences a 

 ferment, converting the starch of the seed 

 into a gummy substance called dextrine, — 

 the true sap of the plants. It is the chemi- 

 cal change which takes place in malting, 

 converting the simple nutriment of the 

 barley into that which, on being brewed, 

 affords the nourishing, though intoxicating- 

 beverage of ale or porter ; or, when dis- 

 tilled, affords ardent spirits. This power, 

 called, in chemistry, catalysis, may be fur- 

 ther illustrated by the leaven used in 

 baking, which is known to every good 

 housekeeper, as " a little leaven leaveneth 

 the whole lump." 



Now the roots contain an immensity of 

 the proper juices of the plant ; nay, the 

 proper juice is here in its most concentrated 

 or inspissated state ; for, if we examine a 

 plant, we shall find that while its proper 

 juice is mild in the leaves, it is stronger in 

 the twigs and branches- — stronger still in 

 the bark of the trunk, — but still more con- 

 centrated in the root. Now, it is by tho 



