OP THE ELEMENTARY STRUCTURES. 727 



of much dispute from an early period, and have been repeatedly 

 investigated. Hales, BischofF, and others, came to the conclu- 

 sion that, these vessels were carriers of air ; while Dutrochet, 

 Link', Kominger, &c., believed that their essential function was 

 to carry fluids from the root upwards. According to Link, Avhen 

 plants are watered for several days with a solution of ferro- 

 cyanide of potassium, and afterwards with a solution of per- 

 sulphate of iron, prussian blue is found in the vessels, and not 

 in the prosenchymatous cells, as the experiments of Hoffman 

 alluded to in speaking of the functions of prosenchymatous cells 

 would seem to prove (see page 726). The opinion now more 

 generally entertained is, that the vessels in their normal con- 

 dition in the regular course of vegetation contain air, but that 

 when plants are gorged with fluids, as in the spring of the year, 

 they, as well as the prosenchymatous cells (the usual carriers of 

 fluids), are filled with sap, and assist in its diffusion throughout 

 the plant. 



Functions of Laticiferous Vessels or Canals. — The physio- 

 logical importance of these vessels has given rise to much dis- 

 cussion, and is at the present time involved in obscurity. 

 Nothing further is absolutely known, than that they contain a 

 watery granular fluid which becomes milky on exposure to air, 

 and to which the name of latex has been given. (See p. 37.) 

 Lindley, and some other authors, believe, that they " convey the 

 elaborated sap of a plant to the places where it is needed, and 

 especially dovra the inner part of the bark of Exogens." 

 Schultz called the tissue formed by the ramifications of the 

 laticiferous vessels, cinenchyma, because he believed that he had 

 discovered in it a peculiar vital movement or circulation of the 

 latex, to which he gave the name of cyclosis. This movement 

 may be generally observed, by placing a leaf of the common 

 Celandine (Chelidonium majus), previously dipped in oil, under 

 the microscope, and is described by Balfour " to resemble in 

 many respects the appearance presented by the circulation in 

 the web of a frog's foot." We haA-e, however, never succeeded 

 in observing such an evident circulation in any. laticiferous 

 tissues examined by us, although we agree with Schultz, Balfour, 

 Carpenter, and others, that a kind of vital movement of the 

 latex does occur in the uninjured plant. Amici, Treviranus, 

 Mohl, Henfrey, and others, altogether deny the existence of any 

 such a movement in uninjured tissues, and describe the circula- 

 tion as depending " upon a disturbance of the equilibrium by 

 external causes, such as pressure and heat, and may be pro- 

 duced at will in any direction by making an incision, towards 

 which the juice flows." Further investigation is, therefore, 

 necessary, before we can come to any positive conclusions upon 

 this subject. 

 , Recently, Trecul has propounded a new theory as to the 



