FUNCTION.] CYCLOSIS. 337 



easy to observe a translation of fluid, and to appreciate 

 its rate of motion, by the time which the globules take 

 in moving a certain space. In cases where the motion of 

 cyclosis cannot be actually seen in the vessels, it may be 

 inferred from the following fact. When the two ends of a 

 stem containing milk are cut through, the latex is seen to 

 run out at both ends of the fragment, which proves that there 

 must be both an ascending and descending current : the same 

 phenomenon is visible in plants having a colourless latex ; 

 therefore there must be a motion of ascent and descent in 

 them also. 



2. It occurs in the greater part of monocotyledonous and 

 dicotyledonous plants, and the vessels in which it takes place, 

 are so generally in connection with spiral vessels, that the 

 presence or absence of the one is usually accompanied by 

 that of the other. The situation of the vessels in which it is 

 found is, in the root, stem, petiole, peduncle, flower, &c. 

 The system of vessels, in the form of a delicate network, 

 surrounds the cells, and even traverses their interior, in the 

 most 'diverse directions. In the stems of monocotyledons, 

 cyclosis occurs in the woody bundles, as also in those dico- 

 tyledons which have their wood in like manner separated 

 into distinct cords. But, in the stems of dicotyledons where 

 the wood is disposed concentrically, the vessels of the latex 

 are either placed singly, in the parenchyma of the bark; 

 or, which is most common, they either form a continuous 

 envelope around the wood, or bundles arranged circularly, or 

 even scattered cords. Vessels of latex may even be found 

 in the pith. Schultz finds them in communication with the 

 curious glands which in Nepenthes line the pitcher, and 

 secrete the water found therein. In the form of capillary 

 vessels (vasa contracta), they are very commonly present in 

 hairs, where they form a most delicate plexus. It is, how- 

 ever, difficult to prove that the streams visible in hairs are 

 really ramifications of cinenchyma, and Meyen has even 

 denied their existence, upon which M. Schultz says with 

 some asperity : " Wonderful enough, he has had them before 

 his eyes, everywhere, in the fine anastomosing streams in 

 which the sap circulates in the cells, without recognising 



TOL. II. Z 



