312 



CONSERVATIVE ORGANS, 



[LECT. vn. 



be perceived by the naked eye, or by the aid of an 

 ordinary lens ; but when the microscope is em- 

 ployed, the vessels can be traced from one joint 

 to the other, passing through the spongy cellular 

 diaphragm, and pursuing their course to the sum- 

 mit of the stem. To illustrate this, I have ad- 

 joined (see marginal cut) a 

 plan of the vessels in the knot 

 of the Wheat stem, as dis- 

 played by the microscope, in 

 a longitudinal slice of a straw. 

 In this plan the white lines 

 a. . represent the course of 

 the vessels in the cylindrical 

 part of the old joint running 

 in a perpendicular direction, 

 which they preserve up to the 

 point b. b. where the leaf se- 

 parates from the new articu- 

 lation c. which is sheathed within it. At d. d. and 

 between that point and b. b., branches are given 

 off, which meet in the centre of the cellular matter 

 of the knot, and again join the vessels a. a. at . 

 b. b. where they enter the leaf f.f. in which they 

 terminate. A little lower, however, opposite g. g. 

 vessels are sent off, which at first are curved in- 

 wards, but soon acquire a perpendicular direction 

 and constitute the vessels of the new joint as seen 



