Leading Principles of the Growth of Trees. 



il 



to the success of a crop. The seeds of noxious weeds remain many 

 years buried beneath the soil, until cultivation brings them up, mixes 

 them with the soft mellow surface, accessible to air, when they spring 

 up in profusion over the ground. 



As a general rule, seeds germinate and grow most readily when 

 buried to a depth of from three to five times their diameter, in soils 

 of ordinary moisture. 



In order to produce germination, moisture must find ready access 

 to the interior of the seed. It is often excluded, if the coats have 

 been allowed to become too dry. The thick coverings of the chest- 

 nut, horse-chestnut, and many seeds of similar character, if left a 

 few days exposed to the air. become so hard as to prevent it. To 

 secure success, they must be kept moist by imbedding them in moist 

 sand, leaf-mould, or moss, from the moment they- separate from the 

 tree until planted in the earth. Apple seeds and some others, which 

 have been allowed to become too dry, may frequently be started by 

 scalding and then exposing them to the action of the frost ; and by 

 repeating the process several times, there is greater certainty of ger- 

 minating. As the scalding and cooling must be quickly done, por- 

 tions not larger than two or three pounds should be taken at a time. 

 The object in cracking peach and 

 plum-stones before planting, is to 

 admit air and moisture a process 

 which is also hastened by subject- 

 ing them to freezing and thawing. 



The Structure of the Plant or 

 Tree. All plants, in the first place, 

 are manufactured or built up of 

 innumerable little cells, sacs, or 

 cavities. These are usually not 

 over a five-hundredth part of an 

 inch in diameter, and in many plants 

 they are still smaller. Fig. i ex- 

 hibits a small part of the young 

 shoot of the peach, cut across the 

 whole shoot presenting at least 

 10,000 of these little vessels, only 

 visible under a good microscope. 

 The branch of an apple-tree, an 

 inch in diameter, cut across, shows about one million. This cellular 

 structure exists throughout the roots, stems, shoots, leaves, flowers, 

 and fruit 



Fig. i. 

 Cross-section of the sap-vessels 



of 



young shoot of a peach, greatly mag- 

 nifieda, bark ; b, wood; c, pith. 



