The Plantlet. 37 
plants. The earlier seedlings overtop the later and feebler 
ones, and so crowd them out of existence. We should pro- 
fit by this hint and reject the later plants in the seed-bed. 
51. How Deep should Seeds be Planted? We have 
seen (29) that one object of planting seeds in the soil is to 
place them in contact with moisture. Since the plantlet 
must force its way through the soil that covers the seed, the 
less the depth of the 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 sufficiently 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. 
52. 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 
frequently and carefully watered with a watering-pot having 
a very fine rose. When small seeds are sown in full expos- 
ure to sunlight, it is well to shade the surface with paper or 
a muslin-covered frame, to check evaporation until the 
plantlets appear. Sometimes small seeds are covered with 
a very thin layer of sphagnum moss, that has been rubbed 
through a sieve. This helps to retain moisture in the sur- 
face soil. 
53. Ferns are Grown from Spores* sown on the sur- 
* Spores are the chief reproductive bodies in plants that produce no seed, as 
ferns, mushrooms, mosses, etc. They are usually so small as to be barely visible 
