CIRCULATION IN PLANTS. 41 



surface. Many aquatic plants, as the BatrachospcTjnum, 

 are, in like manner, protected by a viscid layer, which ren- 

 ders the leaves slippery to the feel, and which is impermea- 

 ble to water. 



Several tribes of plants contain liquids that are opaque, 

 and of a white milky appearance: this is the case with the 

 Poppy ^ the Fig-tree, the Convolvulus^ and a multitude of 

 other genera; and a similar kind of juice, but of a yellow 

 colour, is met with in the Chelidonium, or Celandine. All 

 these juices are of a resinous nature, and usually highly 

 acrid, and even poisonous in their qualities; and their opaci- 

 ty is occasioned by the presence of a great number of minute 

 globules, visible with the microscope. The vessels in which 

 these fluids are contained are of a peculiar kind, and exhibit 

 ramifications and junctions, resembling those of the blood 

 vessels of animals. We may also discover, by the aid of 

 the microscope, that the fluids contained in these vessels are 

 moving in currents with considerable rapidity, as appears 

 from the visible motions of their globules; and they present, 

 therefore, a remarkable analogy with the circulation of the 

 blood in some of the inferior tribes of animals. This curious 

 phenomenon was first observed in the Chelidonium by 

 Schultz, in the year 1S20; and he designated it by the term 

 Cyclosis, in order to distinguish it from a real circulation, 

 if, on farther inquiry, it should be found not to be entitled 

 to the latter appellation.* 



The circular movements which have been thus observed 

 in the milky juices of plants, have lately attracted much 

 attention among botanists: but considerable doubt still 

 prevails whether these appearances afford sufficient evi- 

 dence of the existence of a general circulation of nutrient 

 juices in the vegetable systems of those plants which ex- 

 hibit them; for it would appear that in reality the ob- 

 served motions of the fluid, are, in every case, partial, and 



* "Die Nutur der Icbcndig-en Pflaiize." See, also, Annulcs dcs Sciences 

 Naturellcs, xxiii. 75. 



Vol. II. a 



