20 INTRODUCTION. 



out horizontally; ascending, when growing obliquely upwards; erect, 

 when growing from the base of the cell directly upwards; pendulous 

 when growing from near the top of the cell; and suspended, when hang- 

 ing directly from the summit of the cell. 



Let us consider now more especially the Seed, as we find 

 it developed from the fertilized ovule. We will find that 



_ 106. The Seed Coats are commonly two, the testa and 



FIG. 37. the tegmen. The testa is the outer coat, originally the 

 primine of the ovule, and often becomes very greatly changed 



in process of development. It may be thin and papery, or thicken and 



become very hard or woody, etc., and be smooth or variously marked. It 



may send out membranous projections, to serve as wings, or hairs (Figs. 



37-39), etc. devices for rendering the 



seeds buoyant, that the wind may 



more widely scatter them, as they fail 



from the pods which open to discharge 



them. 



107. The tegmen is the inner coat, 



originally the secundine of the ovule, 



and is usually thin and delicate, often 



hardly distinguishable from the testa. FIG. 38. FIG. 40. 



108. The Kernel or Nucleus of the seed comprises 

 all interior to its coats, and consists of either embryo alone 

 or with an accompanying albumen as the case may be. 



1 09. The Embryo or Germ is the rudimentary plantlet, 

 and consists of three parts, usually quite easily distin- 

 guishable. They are the cotyledons or seed-leaves, the 

 radicle, which in germination grows downward and 

 forms the root, and the plumule which develops upward 

 and forms the stem or trunk. The cotyledons usually 

 constitute by far the greater bulk of the embryo, and 

 are more or less gorged with nourishment, prepared 

 food deposited there by the parent for supporting the 

 young plantlet, when at the time of germination it needs 

 it for assistance in taking root in order to " shift for itself/' 

 According as there are one, two or several cotyledons, 



_ seeds are said to be respectively monocotyledonous, dico- 



FicT 39***' tyledonous or polycotyledonous. 



110. The cotyledons as seen in the Horsechestnut, 

 Pea, etc., are very thick and seem very little like leaves. Those of 

 the Squash, Maple, etc., resemble leaves somewhat, and after giving up 

 their stored food in germination rise above ground and serve as leaves. 

 In the seeds of many classes of plants the cotyledons contain but very 

 little nourishing matter, and then 



Fig. 37. Fruit of the Birch a samara with two wings. (From Hough's Elements of 

 Forestry.) 



Fig. 38. Fruit of the Elm a samara winged all around. (From Hough's Elements of 

 Forestry. ) 



Fig. 39. Pistillate catkin of the Poplar, with pods mostly open, and the matured seed ready 

 to escape. (From Hough's Elements of Forestry.) 



Fig. 40. Seed of the Cottonwood showing its hairy tuft. (From Hough's Elements of 

 Forestry.) 



