6 



INTRODUCTORY CHAPTER. 



itself from the latter with its integuments; and when placed under favourable 

 circumstances, it sheds or leaves its coats, and becomes developed into a plant 

 similar to its parent. 



The caulicle (T) is a small cylindric or conical body, bearing the first leaves of 

 the plant (fig. 19, c), which ascends to form the stem. The radicle (R), or organ 

 destined to develop the roots, is at first merely a transparent point terminating the 

 free end of the caulicle, and tending downwards ; it usually corresponds in the seed 

 to the position of the micropyle (figs. 17, 18). The cotyledons (figs. 17, and 19, c), 

 which are the first leaves of the young plant, spring laterall}' from the caulicle, and 

 protect the plumule, or first shoot of the future plant; they are usually thick and 

 succulent, and nourish the young plant until it is able to support itself. Within 

 the integuments of the seed there always exists, at an early period, a peculiar form 

 of cellular tissue, the study of which is important, and to which we shall recur; it 

 is sometimes rapidly absorbed by the embryo, but at others it is retained in the 

 seed until germination, in which case it is called albumen, and supplies the young 

 plant with its first food. 



Considering the embryo as the plant in its simplest form, let us follow the growth 

 and lateral development of its primitive axis. The two first leaves (cotyledon*) are 

 attached to the small stem (caulicle), as may 

 be seen in the Pea (fig. 19), or, bettor, in a 

 germinating Bean (fig. 20, c, c). The radicli', 

 which terminates the free end of the caulicle 

 (fig. 20, T), sends out many descending branches, 

 and forms the root (u). Sometimes the coty- 

 ledon is solitary, as in the Maize (fig. 21, c), 

 when the rootlets usually spring from various 

 points of the caulicle (t), and branch very little. 

 At the point of union of the cotyledons or 

 cotyledon with the cauliclc is the plumule (fig. 

 20, 0,0, and fig. 21, </). Each cotyledon and 

 each leaf of the plumule is produced from a 

 node, but the internodes are scarcely visible. *' G l * onot Mllizc - 

 Soon after germination, as the plant grows and the axis lengthens, the nodes, and 

 consequently the leaves, become separated. Near the flower the internodes of the 

 axis shorten, the leaves usually become smaller and changed in form and colour ; 

 finally, at the termination of the axis, the leaves (flower), instead of forming a 

 spiral or being placed in pairs, are arranged in superimposed whorls of dill'' n-nt 

 structure, the leaves in each whorl usually alternating with those of the next 

 within or above it; which results in the blades of the different leaves composing 

 the flower being separated as far as is compatible with being crowded in a very 

 small space. 



The leaves of the three first floral whorls (sepals, petals, stamens) have no buds 

 in their axils or on their edges ; those of the pistil alone (carpels) produce and 

 protect buds ; each edge of the carpel (placenta) giving origin to cords, which 



; 



20. Germination of Kidney- 



