TISSUE SYSTEMS 



337 



FlCf. 718. 



{fig. 719, h). In the leaves ofoertain Monocotyledons it consists of 

 aqueous tissue, being made up of thin-walled parenchymatous 

 cells which contain little more than water, and are packed close 

 together without intercellular spaces. Some succulent leaves 

 have their ground tissue entirely composed of this. 



The general ground tissue shows a peculiar character in 

 foliage leaves, the cells, 

 though parenchymatous, 

 not being at all like those 

 of the stem. On one or 

 both sides they are found 

 to be elongated and ar- 

 ranged in one or several 

 rows, with their long axes 

 at right angles to the sur- 

 face. They have anumber 

 of ehloroplasts embedded 

 intheirprotoplasm. From 

 their mode of arrangement they have been ca,\\e A palisade tissue 

 {fig. 720, p.t.). If this tissue is only on the upper side of the 

 leaf, the lower side shows more irregularly arranged chlorophyll - 

 containing tissue which from the looseness of its arrangement 



Fiff. 718. Outer part of root of Hyafiiuth. 

 ep. Epiblema. pr. Exodermis. c. Cortex. 

 X 250. 



Fig. 720. 



Fig. 719. Portion of transrerse section of leaf of riaii.^. e. Epidermis. !i. 

 Hypoderma, Fuj. 720. Section of leaf of Beta. e. Epidermis, p.t. Pali- 

 sade tissue. s.p. Spongy parenchyma. 



has been caHeA spongy parenchyma {fig. 720, s.^).). It is chiefly 

 remarkable for its abundant intercellular spaces. 



The general ground tissue of the cortex may contain many 

 other kinds of tissue already described ; resin ducts, laticiferous 

 tissue, &c., aU ocotu- in different plants. 



Crossing the cortical tissue of the stem we find fibro- vascular 

 strands joining the meristeles of the leaf with the main axial 



VOL. I. Z 



