128 Elementary Principles of Agriculture 



special requirements of the crop. Quick-growing annuals 

 and root-crops do best on a very loose seed-bed. Sugar 

 beets become fibrous, and may be pushed out of the 

 ground if the roots reach a hard subsoil. The depth of 

 covering the seeds often has a great influence not only 

 on the promptness of germination, but, also, on the 

 fruitfulness of the crop. The distance between the seeds 

 must be such that there is proper room for the develop- 

 ment to the size desired at maturity, or for transplant- 

 ing.* 



192. Propagation by Seedage and by Division Com- 

 pared. The embryos in seeds are formed by the union 

 of the nuclei of pollen and egg-cells, each from differ- 

 ent individuals. In division, the new individual is 

 formed from a part of the original plant, and, therefore, 

 has only the characters of the original plant, that is, it 

 is just like the original plant. Seed-propagated plants 

 often partake of the characters of two individuals. 

 This explains why seed-propagated plants are more 

 variable than those propagated by division. For illus- 

 tration, we may use blackberries. Fig. 77 shows the 

 forms of the leaves of a number of blackberry plants 

 grown by Luther Burbank from seeds of a single plant. 

 Not all seeds are so variable as the example given, but 

 they are, in most cases, variable, and the differences are 

 only of degree. Therefore, in order to make sure of propa- 

 gating the desirable qualities of some particular indi- 

 vidual, resort is had to propagation by division. 



193. Propagation by Division may be by some of the 



*NOTE. It is not advisable to discuss the needs of particular crops in a 

 general text-book, but a number of interesting comparisons may be made in 

 this connection by comparing (1) the season of seedage; (2) depth of planting and 

 size of seed ; (3) how the depth of planting affects the potato crop ; (4) the 

 duration of the roots in the soil; (5) surface feeding and deep-feeding or tap- 

 rooted plants. 



