The Rev. P. Keith on the Internal Structure of Plants. 289 



beFs account of the vessels of plants that Dutrochet has not 

 got something to object to. 



But as M. Dutrochet may be thus said to have demolished 

 the superstructure of M. Mirbel, it was but fair that he should 

 substitute something in its place. This he has accordingly 

 done upon the firm and legitimate basis both of observation 

 and experiment; so that instead of the vessels of Mirbel, 

 which seem to have been multiplied into too many species, 

 we have now the following, as exhibited by Dutrochet*. 

 1st. Globule-bearing tubes, or lymphatics, les vaisseaux corpus- 

 culifercs. They abound in the wood, and particularly between 

 the concentric layers of different years. They are studded 

 with small globules, or molecules, that are imbedded in their 

 walls, and they conduct the ascending sap. 2dly. Spindle- 

 shaped tubes, or clostres. They consist of a longitudinal suc- 

 cession of small tubes, swollen in the middle and pointed at 

 the extremities, and often divided by transverse diaphragms. 

 They are destitute of globules. They conduct the cambium, 

 or descending and elaborated juice, partly through the chan- 

 nel of the alburnum, but chiefly through that of the bark. 

 3rdly. Spiral tubes, or tracheae. These Dutrochet describes 

 as approaching pretty nearly to the true spirals of Mirbel, 

 with the exception of their being furnished with globules end- 

 ing in conical spires ; but he assigns to them a different func- 

 tion, namely, that of conveying to the interior of the plant a 

 vivifying fluid, the product of insolation. 4thly. Proper ves- 

 sels, les vaisseaux propres. They are found both in herbaceous 

 and woody plants. They have a great comparative width of 

 diameter. They convey the descending and secreted fluids, 

 such as the milky juice of the Fig or Spurge, and yellow 

 juice of the Celandine, and differ from the lymphatics chiefly 

 in being destitute of globules. 5thly. Articulated cellular 

 tubes. They consist of a series of united cells assuming a 

 tubular form, sometimes longitudinally, and at other times 

 transversely, forming the divergent layers. They are regarded 

 by Dutrochet as an emanation from the pith. They seem to 

 correspond to the cellular tubes of Mirbel; but in place of 

 being furnished with pores, we are to regard them as being 

 furnished with globules. 



Thus we have reached and inspected the ultimate and ele- 

 mentary organs of which the whole fabric of the plant is com- 

 posed ; and if it is asked of what the elementary organs are 

 themselves composed, the reply is, they are composed, as 

 appears from the same analysis, of a thin, colourless, and 



* Rccherckes Anatomiques, sect. i. 



Third Series. Vol. 5. No. 28. Oct. 1834. 2 P 



