LATICIFEROUS VESSELS, ETC. 1 75 



organisation of the body to be recognised. Like the segmented laticiferous vessels, 

 these unsegmented tubes may also send forth branches from the cortex across 

 through the vascular bundles and secondary wood into the pith, in which they 

 ramify all over or chielly in the outer part. By maceration it is possible to free 

 the ends of their branches in the growing points and leaves, and to convince 

 oneself of the fact that we have here to do with continuously growing free ends of 

 individual tubes, and not with the fusion of originally separated cells, as in the 

 segmented laticiferous vessels. The walls of the thicker, older latex tubes, especially 

 of the Euphorbiae, may attain a very considerable thickness. 



While the finer ramifications of both kinds of laticiferous vessels are inserted 

 between the most various tissues within the organs, the tendency prevails for the 

 main stem of the tubies to accompany the vascular bundles, and especially to run 

 in the neighbourhood of the sieve-tubes, or even to replace them. This is espe- 

 cially striking where the laticiferous vessels in the secondary cortex arising from 

 the cambium are the more numerous the fewer the sieve-tubes, or vice versa {Papaver 

 B-hocas, Argemone viexicana, Chelidoniian rnajus, and Glauciuin luleum, according to 

 De Bary). 



The laticiferous vessels contain, as stated, two essentially different groups of 

 substances; those which are again utilised in metaboHsm (proteids, carbo-hydrates, 

 fats, ferments), and those which must be regarded as excreta useless in metabolism 

 (resins, gums, caoutchouc, alkaloids, etc.). 



The Receptacles of Secretions, now to be considered, and which should more 

 properly bear the name of excretory organs, contain on the other hand exclusively 

 auch matters as find no further use in the metabolism of tlie living plant. This 

 may be concluded with certainty from the fact that when these matters have once 

 arisen in a' given receptacle, they remain there, and are not again dissolved and 

 used for the purposes of growth. It is not implied that these matters produced 

 as bye-products in metabolism are completely useless to the plant, like the refuse 

 in chemical works; they may, rather, according to circumstances, be of use 

 for the well-being of the plants concerned in this or that sense. This is particularly 

 well seen in many epidermal glands, to be described later. It is only to be insisted 

 on here that the matters referred to are not further concerned in the nutritive 

 processes and metabolism accompanying growth. Since such substances, as already 

 mentioned, also accumulate in the laticiferous vessels and become withdrawn from 

 the processes^ of interchange of fluids, it is intelligible that, with few exceptions, the 

 plants provided with laticiferous vessels possess none of the receptacles for secretion 

 here to be described ; and also that the presence of the latter generallv precludes 

 that of laticiferous vessels (De Bary). 



The refuse matters collected together in the receptacles for secretions are, from 

 a chemical point of view, of very various nature. Calcium oxalate, in the form 

 of beautiluUy constructed crystals or crystalline granules, occurs very commonU-, 

 especially in Phanerogams. More confined to single orders and families are found 

 resins and ethereal oils, both usually combined into a so-called lialsam : mucus, 

 swelling in water, and various kinds of gums also occur, and these, when they 

 are accompanied in the receptacles for secretions In- resins and ethereal oils 

 and form emuUions in water, resemble latex. Fmm the presence of these 



