the Vasa propria, and Beceptades of the Juices of Plants. 269 



of coloured liquid escapes from the section of a plant which has 

 been plunged for a few seconds in boiling water. [This seems, 

 to our mind, not to prove the effects of death simply on the 

 escape of the laticiferous fluid, but to show the coagulability of 

 that fluid by the heat employed. In other words, is not the 

 retention of the fluid a consequence of its coagulation by heat ? 

 — Trans.] 



A very high importance should therefore be assigned to the 

 coloured juices and to the apparatus which contains them, if this 

 structure be found to present a uniform character in all those 

 •plants which are provided with laticiferous fluid. Let us there- 

 fore inquire whether this system possesses in its organization 

 that character of uniformity which the general function attri- 

 buted to it seems to demand. In other words, have all lactescent 

 jjlants a vascular system ? 



We have already remarked that vasa propria are more scarce 

 in certain parts of lactescent plants than in others, and that 

 they are not met with at all in some of their important organs, 

 and notably in the roots. For example, these vessels, which 

 occur so plentifully in the stem of Asclepias syriaca, are infre- 

 quent in that portion of the stock which is furnished with buds, 

 and are nearly or altogether wanting in the inferior part of this 

 organ. 



Moreover the proper vessels may become altered in character, 

 and, so to speak, lose their primitive conformation, their con- 

 tinuity, their divisions, and their anastomoses. 



In Sambucus EbuJus I have met with, in the bark and medulla, 

 rigid, isolated, straight, and thick-walled tubes, which contained 

 a coloured substance of considerable consistence, that became 

 of an intense red in contact with the air, and was collected in 

 irregular masses, grouped confusedly. These tubes were cer- 

 tainly more like fibres than vasa propria, nevertheless they 

 contained special juices. I have also seen the like in Sambucus 

 nigra, except that here the contained matter was less deep in 

 colour. 



In Ferula tingitana, and in several plants of the family Um- 

 belliferse, the proper juices are likewise contained in thick- walled 

 tubes. 



On approaching the roots, the reservoirs of coloured juices 

 are found to change their nature. Thus in Chelidonium majus 

 the yellow juices of the stem circulate in long and continuous 

 vessels, whilst in the root the juices, which have acquired an 

 orange-colour, are contained in cells of greater or less thickness, 

 united end to end, so as to form irregular fibres. Further, in 

 several Convolvulacese the coloured juices in the roots are found 

 collected in utricles — a circumstance observed in the external 



