. STEMS AXD THEIR APPENDAGES. 57 



second and third pair of the true leaves unfold, the seed- 

 leaves below commence to dry up, as shown in the seed- 

 ling Maple, figure 15, and eventually drop off. 



The position as well as the movements of cotyledons 

 in seedlings are characters worthy of careful study by 

 cultivators of plants, for it is quite important to know 

 in advance of sowing seeds whether the first leaves are 

 to "come up," as with the Bean, or remain stationary 

 below the surface, as with the Pea, Wistaria, Oak and 

 similar seeds, for in the former the cotyledons must 

 break through the soil and come to the surface, while in 

 the latter it is only a new and slender stem therefrom 

 that appears. Different conditions, therefore, are re- 

 quired for different growths, for the large, _fleshy_seed- 

 leaves of some kinds of plants would never break through 

 a compact soil or crust on its surface that might not 

 seriously impede the progress of plants with cotyledons, 

 which remain stationary at the depth at which they are 

 deposited. 



While the two cotyledons are generally recognized as a 

 characteristic of plants with woody, exogenous stems, 

 still there are some exceptions ; among the most famil- 

 iar of these are the conifers, or cone-bearing trees, for 

 in these the cotyledons or seed-leaves are quite variable 

 in number. In the seedling Arbor-vitae (Thuya), the 

 usual number is two, but in the Pines they range from 

 four and five up to fifteen or sixteen in Sabine's Pine 

 (Pimis SaMniana.) The seed-leaves in the Pines are 

 produced in a whorl, as shown in figure 16, and they 

 always push their way up above the surface, if not pre- 

 vented by a too compact soil. The true leaves of the 

 Pine tree grow in clusters, or, more properly, bundles, 

 the lower ends being encased in a kind of sheath. 



The number of leaves in a sheath varies in different 

 species from one or rarely two, in the One-leaved Pine 

 (Pinus monophylla), up to five in the common White 



