64 



ENDOGENOUS OE MONOCOTYLEDONOUS STEM. 



anoe, as shown in fig. 128, which represents an Irish yew with an 

 anomalous stem. This peculiar appearance is said to be liable to 

 occur in coniferous plants grown from cuttings. A Sequoia (WeUing- 

 tonia) gigantea is mentioned in which a tuberous mass was produced 1 

 foot 6 inches in circumference, on a plant grown from a cutting, the 

 plant being only 3 feet in height, with a stem 2^ inches in circum- 

 ference. 



Fig. 129. 



Endogenous or Monocotyledonous Stem. 



This kind of stem is composed of cells and vessels which are 

 differently arranged from those of the Exogenous stem. The vascular 

 bundles are scattered through the cellular tissue, and there is no dis- 

 tinction between pith, wood, or bark. There are no medullary rays, 

 nor concentric circles (fig. 129). . In the young 

 state, the centre of the stem is occupied entirely 

 by cells, which may be said to represent pith, 

 and around this the vessels are seen, increasing in 

 number towards the circumference. The central 

 cellular mass has no medullary sheath. In 

 some cases its cells are ruptured, and disappear 

 during the progress of growth, leaving a hollow 

 cavity (fig. 130) ; but in general it remains per- 

 manent, and is gradually encroached upon by 

 the development of the vascular system. The 

 latter consists of vessels arranged in definite 

 bundles, which do not increase by additions to 

 their outside after being once formed, although 

 they are developed in dT progressive manner. 

 These bundles may be considered as representing 

 the vascular wedges, produced during the first 

 year of an exogenous stem's growth (fig. 111). 

 They consist of woody vessels enclosing some 

 cellular tissue between them, with spiral and 

 pitted vessels. The outer part of the stem is not formed by a sepa- 

 rable bark, but consists of a dense mass of fibrous tissue, mixed with 

 laticiferous vessels and cells. It is intimately connected to the inner 

 part of the stem, without the intervention of medullary rays. 



On making a transverse section of a young endogenous stem 

 (fig. 131), there is observed a mass of cells or utricles, u, of various 



Fig. 129. Part of the stem of Asparagus cut transversely, showing the vessels as points 

 distributed through the cellular tissue. I, Leaf in the form of a scale. Fig. 130. Trans- 

 verse section of stem of Phragmites communis, or common reed. Tlie cellular tissue in the 

 centre has disappeared, leaving a iistular or hoUow stem, with a ring of cells and vessels, 

 the latter indicated by dots, n, Node where the fibres cross, so as to form a solid partition. 



Fig 130. 



