594 



PHYSIOLOGY. 



In the latter case 



598 



the perisperm, as in most Palms, the Onion, &c. 

 the plumule bursts through a slit 

 in the side of the stalk of the 

 cotyledon, which is protruded 

 from the perisperm. In Orchids 

 and some other plants the em- 

 bryo is at first a homogeneous 

 body without differentiation of 

 parts. The corm of Arum ita- 

 licum is formed from a dilata- 

 tion of the tigellum. In this 

 plant the radicle is first pro- 

 truded as a temporary tap-root, 

 then the long tubular sheath of 

 the cotyledon appears, the blade 

 of the cotyledon being of globu- 

 lar form and retained within 

 the perisperm, as in many other 

 Monocotyledons. At the base 

 of the sheath of the cotyledon 

 may be seen the plumule and 

 the originally small tigellum, 



v i i 11 j 11 _j'i i Germination of Palm. The plumule is seen 



which latter gradually dilates eme f rom the sheath of the cotyledon, 



into a COrm. the blade of the latter being enclosed within 



the seed. 



Sect. 3. DEVELOPMENT OF THE STEM, ETC. 



The general structure, arrangement, and mode of development 

 of the fibre-vascular bundles of the stem, roots, and leaves has been 

 alluded to in previous paragraphs, but in this place it remains to 

 give a general indication of the mode of growth and development of 

 the organs as a whole; and for this purpose reference may be 

 briefly made to the growing-points, or puncta vegetationis, by means 

 of which tl\e growth in length is carried on. 



Growing-points. In the case of Phanerogamia these growing- 

 points are situated at either end of the seedling plant, that in which 

 the direction of growth is upward forming the stem (fig. 599), that 

 in which the direction is downward forming the root (fig. 583, 

 p. 536). The lateral branches originate in similar growing-points, 

 which constitute the essential part of the buds. 



The "buds, in the first instance, are little conical eminences, consisting 

 exclusively of cellular tissue, the constituent cells of which speedily 

 range themselves in three divisions, which may he termed central (plerorne), 

 cortical (periblem), and epidermal series (dermatogen) : p. 515. Of these 

 the central series form the mass of the young hud ; its cells divide at first 



