2 PRINCIPLES OF THE GROWTH OF TREES. 



minute seed, which cannot be planted deep, as the portulacca, 

 must be kept moist by a thin covering or shading. It is often 

 requisite to bury seeds to a considerable depth, in order to 

 secure a proper degree of moisture to start them. On the 

 other hand, they will sprout on the surface unburied, if kept 

 constantly showered. 



The third requisite, air, is an important one. Seeds may be 

 kept dormant a long time by deep burying. Nurserymen 

 have often retained the vitality of peach-stones for a year or 

 two, by burying them a foot or more in compact earth. Other 

 seed might doubtless be kept for a time in the same way. 

 Planting too deep is often fatal 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 cover- 

 ings of the chestnut, horse-chestnut, and many seeds of sim- 

 ilar 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 germinating. As the scalding and cool- 

 ing must be quickly done, portions not larger than two or 

 three pounds should be taken at a time. The object in crack- 

 ing peach and plum-stones before planting, is to admit air and 

 moisture — a process which is also hastened by subjecting 

 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- 



