SCLERENCHVMATOUS FUNDAMENTAL TISSUE. 



147 



Fig. 157. — Transverse section of the stem aiLycoj>odiufn chatnescyparissns 



Plums and Cherries owe their name — stone fruit— to the circumstance that the 

 fundamental tissue of the pericarp, at first homogeneous and parenchymatous, 

 becomes separated into two layers, of which the outer, enclosed by a solid 

 epidermis, forms the edible flesh of the fruit, and the inner one the so-called 

 stone. Each consists af first of thin-walled large parenchyma cells filled with sap 

 containing sugar, while the cells of the tissue of the stone become exceedingly 

 thick-walled, and finally, on ripening, are very strongly lignified. Especially 

 various are the cell-formations 

 in dry fruits, capsules, and in- 

 dehiscent fruits, as well as in 

 the testa of many seeds. It 

 is, however, difficult to give a 

 survey of these forms at all 

 comprehensive, since a com- 

 parative study of them is 

 still wanting ; and we have 

 here to do everywhere with 

 specific adaptations to definite 

 biological relations of indivi- 

 dual species of plants. In the 

 tissue-formations of the coats 

 of seeds and fruits it is some- 

 times simply a matter of solid- 

 ity and mechanical protection ; 

 sometimes of arrangements 

 which, on the ripening of the 

 capsule, bring about its dehi- 

 scence and the scattering of 

 the seeds. Berries and stone- 

 fruits by means of nourishing 

 masses of tissue attract animals 

 'to eat them, and the latter then 

 scatter the hard-shelled seeds 

 at other places. In other cases 

 again, wings or parachute-like 

 outgrowths (Pappus of the Com- 

 posite) arise on seeds or dry 

 fruits ; and many other such ar- 

 rangements exist, which are na- 

 turally connected with peculiar 

 developments of the portions of tissue concerned. 



Among the various forms of fundamental tissue is also to be included one which 

 is the most widely spread and physiologically by far the most important, viz. the chlo- 

 I'ophyll parenchyma of the green parts of plants, and especially of the foliage leaves. 

 With reference to the forms of the cells and the formation of intercellular spaces, the 

 absence of suberisation and lignification, and the usually thin walls and soft contents, 



L 2 



FIG. 157 S. — Part of the transverse section of a \eaX oi Cafttelliajafioiticn. 

 P parenchyma cells with chlorophyll grains and oil drops ; F a very thin vascular 

 bundle \ vii sl large branched sclerenchyina cell, the arms of which are inserted 

 between the parenchyma cells. 



