130 



PART II. THE INTIMATE STRUCTURE OF PLANTS. 



[ 



take place in any plane, as in the development of the anasto- 

 mosing net-work of laticiferous vessels in many plants (e.g. Com- 

 posite, etc.; see p. 141). 



28. Intercellular Spaces are lacunas between the cells of a 

 tissue. They are formed in two ways : either schizogenously, by 

 splitting of the common wall of contiguous cells ; or lysigenously, 

 by the disorganisation of certain cells. They contain either air or 

 certain peculiar substances. 



The intercellular spaces formed schizogenously and containing 

 air, commonly occur in parenchymatous tissue at the angles of 

 junction of a number of cells. The cells of such a tissue, when 

 young, are angular and are in complete mutual contact at all 



points of their sur- 

 face (see Fig. 86) : 

 but towards the 

 close of their growth 

 they tend to assume 

 a more rounded 

 form, with the result 

 that the common 

 cell- walls split at 

 the angles, and thus 

 a system of inter- 

 cellular spaces is 

 formed (Fig. 89). 

 It is a remarkable 

 fact that such inter- 

 cellular spaces as these are exclusively confined to the sporophyte 

 of the higher plants (Bryophyta and upwards). Sometimes these 

 spaces then called air-chambers attain a considerable size, so 

 that portions of tissue are widely separated from each other, as 

 in the petioles of the Water-lily and in other aquatic plants. 



The large air-cavities in the stems and leaves of Juncus and 

 other allied plants are produced lysigenously by the drying-up and 

 rupture of considerable masses of cells ; this is true also of the 

 cavities extending through whole internodes of many herbaceous 

 stems (e.g. Grasses, Umbelliferse, Equisetum), as also of those 

 occurring in leaves (e.g. Leek). 



The intercellular spaces which contain certain peculiar sub- 

 stances are treated of under the head of Glandular Tissue (p. 137). 



FIG. 89. Intercellular ppaces (2) between cells from the 

 stem of Zea Mais ( x 650) ; gw, the common wall. (After 

 Sachs.) 



