74 COMPENDIUM OF GENERAL BOTANY. 



of the fact that the term has become tirmly rooted and that it is 

 used with some degree of justification such a procedure is not ad- 

 visable. It should, however, be observed that wood-parenchjma 

 and medullary rays together form an anatomical-physiological system. 

 From this standpoint, therefore, the ray-parenchyma cells and the 

 wood-parenchyma cells, whether they occur within or outside of the 

 cambium, may be named alike, as is likewise done in the case of the 

 mechanical cells. According to the proposition advanced by 

 Troschel (1879), a pupil of Schwendenek, the entire conducting- 

 parenchyma (medullary-ray tissue and longitudinal bundle-paren- 

 chyma) contained in the conducting bundles might be designated 

 as "amvlome." To me the term fascicular conducting-paren- 

 chyma seems to be preferable, since it at the same time points out 

 the important fact that there is also an extra-fascicular conducting- 

 parenchyma, namely, the parenchyma of the vascular bundle-sheaths 

 (in leaves, petioles, etc.), and the cortical parenchyma of stems and 

 petioles. As already stated, these structures are concerned with the 

 circulation of carbohydrates and physiologically related substances, 

 such as inulin, etc. 



Finally, we will briefly mention the sieve-tuhes with the cam- 

 hiform and conducting-cells. The fundamental characteristic of this 

 tissue is softness, whether the cell-walls are thin or comparatively 

 thick. The ultimate anatomical -physiological difference between 

 cambiform and conducting cells must now be more clearly defined.' 

 These tissues afford a difficult study when considered from the 

 point of mere anatomical desciiption. Sieve-tuhes are usually elon- 

 gated cells with rather thick, sometimes thin, longitudinal walls and 

 horizontal or diagonal transverse walls ; the latter, sometimes also 

 the longitudinal walls, contain minute yerf orations. These thin, 

 perforated cell-wall areas are designated sieve-jylates or sieve-disks. 

 In much-inclined transverse walls there are usually several sieve- 

 plates; in the walls that are horizontal or only slightly inclined there 

 is usually only one. The sieve-plates are perforated and not 

 porous. These openings permit the circulation of undissolved 

 mucous albuminous substances. 



The accompanying figure (43) shows the structure of a trans- 

 verse wall which has been converted into sieve-plates. This figure 



' See DE Bary, Comparative Anatomy. "Wilhelm, Janczewski, and other 

 authors have carried on special researches concerning sieve-tubes. 



