the Vasa propria, and Receptacles of the Juices of Plants. 341 



masses or meati, or vasiform or irregular lacunse. Consequently 

 these reservoirs cannot be said to possess the characters of a 

 vascular system; indeed, when they have unquestionably the 

 form of vessels at their origin and during the greater portion of 

 their course, they are not distributed in the manner of vessels 

 in the organs in which they terminate. It must, moreover, be 

 added that they are not met with in the generality of plants, 

 nor in all portions of the plant in which they may occur. For 

 instance, they cease to exist in the roots of Asclepias Syriaca. 



A still more remarkable condition may be seen in the Acer 

 campestre. In this tree the bark of the young stems and the 

 young branches possesses an abundant lactescent fluid, contained 

 within wide flexuous vessels difficult of detection in consequence 

 of their being surrounded by cells filled with rather greenish 

 granules, not coloured blue by iodine. On tearing, however, a 

 fragment of bark, extremely slender threads ai*e seen interposed 

 among the cortical fibres, and to be very extensible ; these are 

 nothing else but the laticiferous fluid itself, coagulated into a 

 solid substance, eminently elastic, which is drawn out into very 

 delicate filaments having various bulgings here and there, and 

 accurately corresponding in appearance to vessels when said to 

 be in a " state of contraction.^' In portions of the cortical tissue 

 of sufficient transparency, the real vessels are visible, and are 

 seen to be very different from these fibres, and, among other 

 things, to possess walls, which are scarcely distinguishable from 

 the liquid they enclose. Their appearance is so singular that 

 there is little question that they are the structures which have 

 been described (with little precision, indeed) as the laticiferous 

 vessels of the Acer platandides. 



The existence of vasa propria in young stems cannot certainly 

 be called in question; but those layers of the bark which are 

 more than three or four years old are deficient of them, and 

 they are not discoverable in the roots. Hence in old stems and 

 in roots, the new tissues which belong to the same formation in 

 regard to age as do the most recent branches exhibit no traces 

 of laticiferous juices, although these are abundant in the tissues 

 produced in the course of the same year. 



The laticiferous juice, therefore, is not an essential element 

 in the growth of plants. It is sometimes wanting in the most 

 essential portions of plants. It, moreover, is found in certain 

 species, and disappears in others closely allied : thus, the Acer 

 platandides has a perfectly milky juice, whilst the -4cerjoseMc?o- 

 platanus, which is so closely related to it, possesses juices of a 

 perfectly limpid character. The same observation may be re- 

 peated with respect to the Umbelliferse. Consequently the 

 coloured juices cannot be considered agents indispensable to 



