STRUCTURE.] SCHLEIDEN's THEORY. 229 



pyramidal laminated arese. This approximates the cortical 

 integument of Endogens very little to true bark, which is 

 essentially characterised by being separable from the wood ; 

 and having its woody tissue parallel with that of the stem, 

 and formed altogether in an independent, though parallel 

 direction. The apparent bark of Endogens is, in fact, 

 analogous to the mesophloeum and epiphloeum, or cortical 

 integument of Exogens. 



Schleiden's Theory of Stem Formation. 



The views of this Botanist are so peculiar that they 

 demand a separate place. I accordingly give the substance 

 of his theory, from his paper Uber die Anatomisch-physio- 

 logischen Verschiedenheiten der Siengelgebilde, published in 

 Wiegman's Archiv. for 1839, p. 219. Schleiden expresses his 

 surprise that among the numerous controversies which have 

 arisen as to the differences between monocotyledonous and 

 dicotyledonous stems, comparisons should be generally con- 

 fined to the so-called woody trunks of Palms, and those of 

 the common dicotyledonous forest trees of Europe, botanists 

 having, in doing thus, brought into comparison things which 

 are wholly dissimilar. A Palm-stem originates from un- 

 developed interfoliar organs ; but dicotyledonous woody stems 

 from fully developed parts ; a distinction of such importance 

 in plants furnished with numerous series of woody bundles, 

 that the stalk of a pink, and the culm of a grass, do not 

 differ so much as the latter and the axis of a bulb. 



The following differences usually occur in stems, and 

 depend upon various modes of the development, arrangement, 

 and structure of woody bundles. 



I. The woody bundles always grow from the interior to the 

 exterior, and are either LIMITED or UNLIMITED in their 

 growth. In general every woody bundle consists of three 

 parts, having a different physiological value, of very delicate 

 tissue, rapidly formed and of most tender texture, in which 

 new cells are continually generated, and deposited in various 

 ways ; some directed towards the exterior, in the shape of a 

 peculiar tissue having long very thick-walled cells, (liber,) 

 and others towards the interior, in gradual succession, in the 



