20 MORPHOLOGY, OR COMPAEATITE ANATOMY. 



and the roots arise a long way up the stem ; here also the older roots and 

 the "base of the stem decay, so that the whole plant comes to be supported 

 by the lateral adventitious roots, as on so many props. Aerial roots 

 becoming organs of attachment may be seen in the climbing stems of Ivy, 

 of the garden Bignonia (Tecoma radicans), &c. 



Parasitic Plants developed from seeds present, in their earliest stages, 

 a radicle which in some cases becomes developed, in others not, or only in 

 a peculiar manner. Some germinate in the usual way, in the earth, and 

 their roots seek out those of their proper nurse plants, to which they 

 attach themselves organically, others superficially or by penetrating deeply 

 into the interior ; in such cases they may be wholly parasitic, as in the 

 leaflets Broom-rapes (Orobanchacece] , or only partly dependent, as in 

 Thesium, Rhinanthus, and Melampyrum. Others germinate in the usual 

 way in the soil ; but their young stems attach themselves to those of 

 other plants by adventitious roots developed at the points of contact, while 

 the lower part of the parasite, connected with the ground, soon dies away, 

 as in the Dodder (Cuscuta). The woody parasites, Mistletoe (Fwcwm), 

 Myzodendron, and others, are developed from seed upon the spot where 

 they are attached. In the Mistletoe, the seed clings by its viscid pulp ; 

 in Myzodendron by coiled hairy arms ; and when the radicle sprouts, it 

 drives its way through the rind of the nurse plant until it reaches the 

 cambium layer, where it connects itself organically, becoming grafted 

 exactly like a budded rose. No further development of root-structure 

 occurring here, the full-grown plant appears rootless, and like a branch or 

 graft upon the nurse tree. The earlier stages of growth of the Rhizanthese, 

 root-parasites composed chiefly of inflorescence, are not known j probably 

 they are analogous to those of Viscum in the first instance, but with the 

 addition of horizontal growths of stem-structure beneath the 'bark of the 

 nurse plant. 



Characters presented by the Eoot, &c. The points to be spe- 

 cially attended to in studying and describing the root, such as the 

 form, ramification, &c., may be gleaned from what has been before 

 stated and from the Section on the Description of Plants. 



Sect. 3. THE STEM. 



Definition. The stem is the ascending portion of the axis of a 

 plant. It is usually characterized by its growth taking place in 

 a direction contrary to that of the roots, and by bearing on its sides 

 regularly arranged leaves or modifications of leaves, forming the 

 lateral or appendicular organs. The term caulome is applied in a 

 comprehensive sense to any stem or branch or to any modification 

 of those organs bearing leaves or modified leaves, pliyllomes. 



Exceptions. An exception to the ascending growth occurs in the case 

 of creeping stems, where the main axis takes a more or less horizontal 

 position ; but the first shoots of such plants, developed from their seeds, 

 ascend, and the secondary axes, which bear the efficient leaves, assume the 



