HUUE XuL) 1 A'l JuliAuOlLs. Vi 



sam-e oi' all of ilieiu are develepctl, i'ormiiig leafy divisions of the axis, ^^-Iiicli thus 

 Isecomes branched. 



b. Buds are said to be advent itious ^vlicn they are neither tciininal nor axillaiy, 

 Sucli buds generally result from some unnatural condition of t!ie plant, as maini- 

 ing or disease, fend may be formed in the intcrnodes, or upon the roots (140), 

 or from the hunk, or even from the leaves, as in tiie Bryophyllum. 



170. A BKANCii, tlicrcfoic,?^s a diYision of the axis, produced 

 Ijy the development of an axillary hiid. ■ 



171. A THORN, or spine.' is a leafless, hardened, pointed, 

 woody process, with which some ] )lants are armed, as if for self- 

 defence. Ex. CratEEgus, locust. ; 



a. The thoni appears to be /an abortiA'e growtli of a bud, I'esulting from the im- 

 perfect development of the growing -poml only, while its leafy coverings perishJ; 

 ■Soma plants which naturally produce thonis become thornless by cultivation. 



|ln such cases the buds are enabled, by better tillage, to produce branches instead 

 ■of thorns. Ex. apple, pear, goosebei-ry. / 



b. The thorn is distinguished from the prickle (43) by its woody structure, and 

 its connection with the wood of the stcni, while the prickle, as of the rose, consists 

 •of hardimed cellular tissue, connected with the bark only." 



172. That point in the stem where the leaf, with its axillary 

 bud, is produced, is called the node, and the spaces between 

 them the inteknodes. 



a. In the internodos the fibres of the stem ai'o parallel, 'but at the nodes this 

 order is intemipted in consequence of some of the inner fibres being sent off later- 

 ally into tiie leaf-stalk, occasioning, more or less, a jointed appearance. Hence, 

 also, each interi;ode contains fewer fd)re3, and is of a less diameter than thoso 

 below it, so that the axis gradually diminishes upwards. 



173. Since the blanches arise from axillary buds, their ar- 

 rangement upon the s^em will depend upon that of the leaves, 

 which, in all young plants, at least, are aiTanged with great 

 symmetry and order. 



174. It is a general law in the arrangement of the leaves and 

 indeed of all other appendages, that they are disposed spirally, 

 that is, in a hue which winds around the axis like the threads 

 of a screAV. 



a. But this aiTangement is often so mncli disguised, by distru'blng causes that it 

 can scarcely be recognized.; The most common modification of it is the circular, 

 wliich is readily explained. The spiral line is formed by the union of two 

 motions, the circular and the longitudinal. The latter is produced in the grow- 

 ing plant by the advancement or lengthening of the axis. Now, if the latter be 

 7 



