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 be 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 check evaporation until the plantlets 

 appear. Small seeds are sometimes covered with a thin 

 layer of spagnum 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 pro- 

 duce 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 devel- 

 oped plantlet (53). 



