134 



BOTANT. 



(1.) Parenchyma is the most constant of the fundamental 

 tissues ; it makes up the whole of the interior plant-body in 

 those cases where there has been no differentiation into more 

 than one tissue, and from here, it is present in varying 

 amount in nearly all (if not all) cases up to and including 

 the highest plants. In stems of Monocotyledons it makes up 

 the mass of tissue lying between the scattered bundles, and 

 in stems of Gymnosperms and Dicotyledons it constitutes 

 the pith and portions of the bark. 



(2.) CoUenchyma, when present, as it frequently is in the 



stems and leaves of Dicotyle- 

 dons, is always either in con- 

 tact with or near to the epi- 

 dermis. 



(3.) Sclercnchyma is com- 

 mon beneath the epidermis 

 of the stems and leaves of Bry- 

 ophytes, Pteridophytes, and 

 Phanerogams. It appears to 

 replace collenchyma in parts 

 having greater firmness than 

 that given by the latter. Some 

 forms of sclercnchyma are 

 scarcely to be distinguished 

 from fibrous tissue — e.g., in 

 the hypodernia of pine leaves 

 (Fig. 110, g, i'). It may be 

 that the supposed cases of fibrous tissue among the funda- 

 mental tissues will turn out to be sclercnchyma instead. 



(4. ) Laticiferous tissue may occur, apparently, in any por- 

 tion of the fundamental system of Phanerogamous plants. 



155. — It is thus seen that in general the tissues of the 

 fundamental system are so disposed that the periphery is 

 harder and firmer than the usually soft interior, although 

 there are many exceptions. This general structure has given 

 rise to the term Hypoderma for those portions of the funda- 

 mental system which lie immediately beneath, or near to the 

 epidermis. Hypoderma is not a distinctly limited portion — 

 in fact, it is often diflScult to say how far it does extend ; 



Fig. 110.— Margin of leaf of Hra«»/)i»- 

 aster, tranevorse section ; c. cuticular- 

 ized layer of outer wall of epidermis ; i, 

 inner non-cuLicularized layer ; &, tliiclc- 

 ened outer wall of marginal cell ; g^ i', 

 hypoderma of elongated sclereQchyma ; 

 Pf cliloropliyll-beanng parenchyma ; pr, 

 contracted protoplasmic contents. X 

 800.— After Sachs. 



