DEVELOPMENT OF THE EMBRYO. 



77 



bark of the whole surface takes their place, although the points 

 from which they should arise are distinctly indicated ; nor are they 

 developed at all in the Dodder (135, Fig. 122), and some other 

 parasitic Flowering plants. In all Cryptogamous plants furnished 

 with a distinct axis, or stem, and leaves, this whole 

 structure has to be formed after germination (110, 

 in a manner to be hereafter shown) ; and when 

 formed, the axis grows from its apex only (108), so 

 that there is no primary root. Phaenogamous plants, 

 on the contrary, are developed directly from an 

 embryo plantlet, an axis with its appendages, which 

 already exists in the seed, and which grows both 

 ways in germination ; from one end to produce the 

 stem, and from the other to form the root, thus 

 exhibiting a regular opposition of growth from the 

 first. To understand this, and to obtain the clear- 

 est conception of the plant as a whole and of its 

 mode of growth, we should at the outset attentively consider the 

 113. Development of the Embryo, The Pha3nogamous plant, then, 

 in the early stage at which we begin its biography, is an EMBRYO 

 (Fig. 100) contained in the seed (Fig. 99). The form of this initial 

 plantlet varies greatly in different species. It is often an oblong 

 or cylindrical body, simple at one extremity, and nicked or lobed 

 at the other, as in the case we have chosen for illustration. The 

 undivided, or stem part is called the RADICLE ; it is the rudimentary 

 axis, the initial stem. The two lobes into which the upper end is 

 split are the COTYLEDONS, or the undeveloped first pair of leaves, 

 often named the Seed-leaves. These are often so large as to make 

 up nearly the whole bulk of the seed, as in the pea and bean, or 

 the Apple and Almond (Fig. 97), where the 

 radicle is very short in proportion ; and on 

 separating or taking off one of them the mi- 

 nute rudiments of one or more additional 

 leaves may often be detected within (Fig. 

 98, a). The embryo, therefore, consists of 

 a short axis or stem, crowned with two or 

 more undeveloped leaves, or, in other words, 



FIG. 96. A Duck-weed (Lemna minor, the whole plant), in flower; magnified. 



FIG. 97. Embryo (the whole kernel) of an Almond, the cotyledons slightly separated. 

 98. The same, with one cotyledon taken off, to show the plumule, or minute undeveloped 

 leaves, a, between the two. 



