LECTURE IX. 



THE SYSTEMS OF TISSUES {continued). 



FUNDAMENTAL TISSUE; RUDIMENTARY DIFFERENTIATIONS OF 



TISSUE. 



I CLASS together all the masses of tissue which are enclosed by the epidermal 

 tissue, and traversed by the vascular bundles, under the term fundamental tissue ^ 

 In the younger and still succulent organs, covered only by the epidermis, 

 and the vascular bundles of which have not yet been altered by subsequent 

 growth in thickness, and in organs generally in which the formation of true 

 wood and secondary cortex has not yet commenced, the main mass of the 

 entire substance consists of funda- 

 mental tissue. This is perhaps 

 best seen in an Apple, the whole 

 edible substance of which con- 

 sists of it. The succulent mass 

 of tissue in the leaf of an Aloe, 

 again, apart from the very thin 

 vascular bundles and the epider- 

 mis, is formed entirely of funda- 

 mental tissue. 



The most widely spread, and, 

 as may well be assumed, the primi- 

 tive and typical form of funda- 

 mental tissue, is the ordinary thin- 

 walled parenchyma; in which we 



may at the same time perceive the typical form of all true cell-tissue. The 

 parenchyma cells are usually the largest in the body of the plant; and are 

 either roundish, polyhedral, or elongated and prismatic,* or more rarely pointed 

 above and below. Very commonly, although not quite generally, small, or often 

 very capacious intercellular spaces run between them. The contents consist of 

 living protoplasm with a nucleus; the former, usually small in quantity, forming 



Fig. 148.— Transverse section throug^h the soft parenchyma of the stem 

 of Zea Mays, gw common wall between each two cells ; z inter-cellular 

 space produced by splitting of the waU. 



'■ I first characterised the fundamental tissue as a system of tissue co-ordinated with the 

 epidermis and vascular bundles in the first edition of my ' Text Book' (1868). 



