172 FUNCTIONS OF CELLULAR TISSUE, [BOOK n. 



bark in which the descending current of the sap takes place 

 is also composed of it; and in endogenous plants, there 

 appears to be no other lateral route that the sap can take, 

 than through the cellular substance in which the vascular 

 system is embedded. It must, therefore, be readily permeable 

 to fluids although it has no visible pores. 



In all cases of wounds, or even of the development of new 

 parts, cellular tissue is first generated: for example, the 

 granulations that form at the extremity of a cutting when 

 embedded in earth, or on the lips of incisions in the wood 

 or bark ; the extremities of young roots ; scales, which are 

 generally the commencement of leaves ; the growing point ; 

 pith, which is the first part created, when the stem shoots up ; 

 nascent stamens and pistils ; ovules ; and, finally, many 

 rudimentary parts : in all these at first, or constantly, is found 

 cellular tissue alone. 



It is that from which leaf -buds are generated. These organs 

 always appear from some part of the medullary system; 

 when adventitious, from the ends of the medullary rays if 

 developed by stems, or from the parenchym if appearing upon 

 leaves. 



It may be considered the flesh of vegetable bodies. The 

 matter which surrounds and keeps in their place all the 

 ramifications or divisions of the vascular system is cellular 

 tissue. In it the plates of wood of exogenous plants, the 

 woody bundles of endogenous plants, the veins of leaves, and, 

 indeed, the whole of the central system of all of them, are 

 either embedded or inclosed. 



The action of fertilisation appears to take place exclusively 

 through its agency. Pollen is only cellular tissue in a parti- 

 cular state ; the coats of the anther are composed entirely of 

 it ; and the tissue of the stigma, through which fertilisation 

 is conveyed to the ovules, is merely a modification of the 

 cellular. The ovules themselves, with their sacs, at the time 

 they receive the vivifying influence, are a semitransparent 

 congeries of cells. 



It is, finally, the tissue in which amylaceous or saccharine 

 secretions are deposited. These occur chiefly in roots, as" in 

 the Cyclamen and Beet ; in tubers, as in the Potato and 



