The Plantlet. 39 



place them in contact with moisture (29). Since the 

 plantlet must force its way through the soil that covers 

 the seed, the less the depth of this soil, other things 

 equal, the less energy and the shorter time are required 

 for the plantlet to reach the surface. Therefore, seeds 

 should not he planted deeper than is necessary to insure 

 the proper supply of moisture. 



Small seeds, as of lettuce, celery and carrot, produce 

 such weak plantlets that it is unsafe to cover them suf- 

 ficiently to insure the proper moisture supply in dry 

 weather. "We must, therefore, plant such seeds so 

 early in spring that the soil has not had time to become 

 dry, or if necessarily planted later, we must depend 

 largely upon artificial watering. 



51. Very Small Seeds, as of petunia and tobacco, 

 Should Not Be Covered with soil at all, but may be 

 pressed down into fine loam with a board or otherwise, 

 and must be watered often with a fine-rose watering pot. 

 When small seeds are sown in full exposure to sunlight, 

 it is well to shade the surface with paper or a muslin- 

 covered frame, to cheek evaporation until the plantlets 

 appear. Small seeds are sometimes covered with a thin 

 layer of sphagnum moss that has been rubbed through a 

 sieve. This helps to retain moisture in the surface soil. 



52. Ferns are Grown from Spores* sown on the sur- 

 face of fine soil in a propagating frame (369), in which 



* Spores are the chief reproductive bodies in plants that produce no 

 seeds, as ferns, mushrooms, mosses, etc. They are usually so small 

 as to be barely visible to the unaided eye. The dust that escapes from 

 a puff ball when it is squeezed or from a bunch of corn smut is 

 formed of the spores of these plants. Spores usually consist of a 

 single cell, in which respect they differ materially from seeds, which 

 contain a more or less developed plantlet (53). 



