Plant Physiology, Theoretic and Applied. 341 



man himself. It is no idle statement to say that were these little bodies to 

 be suddenly and universally destroyed or cease for some reason their activities, 

 all life upon the globe would cease as a consequence. These plastids, or green 

 color bodies, are composed of protoplasm, and are colored green by the fluid 

 called chlorophyll which permeates them. Their ofiice is to accomplish, what 

 no chemist has ever been able to do or ever will do, namely, under the in- 

 fluence of sunlight, change the inorganic materials in crude sap into organized 

 carbohydrates, such as starch, sugar, cellulose, and many others. The crude 

 elements needed, as before stated, are simply the carbon in the atmosphere, 

 and the water in the soil when taken up by the root-hairs. But protoplasm 

 -can not exist without a fourth element, namely, nitrogen, nor could it do its 

 work in building up the carboliydrates ; nay, none of the proteids, such as exist 

 in graham flour, beans, lean meat and a host of others, could be formed at all. 

 The starch made in this laboratory in the day, is carried away at all times 

 while the leaves are on the trees, and nourishes not only the leaf, but flowers, 

 stem and root. Truly we may say, therefore, that plant growth is more down- 

 ward and outward, than upward and outward. The wood which always forms 

 above a cut, not below it, on a tree is a further evidence of this. Hurriedly 

 and imperfectly I have attempted to explain to you this wonderful change of the 

 raw materials all about us into the higher elaborated material needed lor plant 

 •growth, and now to a few practical details. 



It is now evident, why. when we cut off most of the roots of a plant, we 

 should also cut down its top proportionally. Remember that no tree can absorb 

 practically any crude sap except through its root-hairs, which are on the ends 

 of the most delicate rootlets. As nearly all of these have been removed when 

 the tree is taken from the soil, very little sap can ascend the trunk till more 

 roots have been formed. If therefore all of the branches, and as a consequence 

 all of the leaves, are left on that weakened tree, they will tend to do too 

 much work for the poor root systepi, and the plant will either die or be injured 

 for many years. On the other hand how are you going to urge the plant to 

 put out plenty of adventitious, or unusual roots, along the cut stubs left when 

 the tree is planted? They can only be formed by having elaborated material 

 sent down to them from above. Just as idle to expect them to form and do 

 their work without tills assistance as it would be to keep alive and at work 

 a lot of coal miners underground without any provisions sent to them from 

 without. The only true sources of supply for these forming roots are, first, 

 from the reserve starch laid aside in stem, branch, and root fragments and 

 turned into digestible sugar under the warming influences of the spring sun : 

 second, new material elaborated by the leaves. Of course, before any leaves 

 appear in spring, the roots must depend upon the first source of supply, but 

 this will soon be exhausted and then there must be abundant leaves to furnish 

 this material. So the proper balance is to make the head of the tree just 

 large enough to do this work and no larger. 



If the plant to be removed and replanted be already in leaf, and especially 

 if it be a large tree, as sometimes becomes necessary, the greatest care should 

 be taken to leave a few strong leaders with their leaves, to cut back all the 

 rest, and to cover their cut ends with tar, wax, or paint, so as to prevent the 

 waste of sap and natural evaporation through the myriad open vessels which 

 Iiave been cut and have not yet healed over. 



The Stem. — There is little to say about the stem which is not already known 

 liy every live orchardist, unless it be where the crude sap ascends, and where 

 descends the true or elaborated sap. Any of our trees have the wood of their 

 trunks naturally divided into two regions, the heart and the sap. The former 

 is dead and practically useless to the tree, save to add strength to the sap- 

 wood in helping it resist the winds, and hold aloft the crown of leaves. The 

 sap is the living wood and it is through this that the water, with its dissolved 

 salts and earthy contents, rises to the leaves. This is apparent to every one 

 who has seen a hallow tree flourishing for years beside a sound one, and only 



