80 



HUTCHINSON'S POPULAR BOTANY 





to 6y] [E. step. 



FIG. 111. LARCH (Larix europceus). 



together with the 



owers. Native or ALPINE EUROPE. 



with parchment, be placed together 

 lengthwise, and holes be driven 

 through the parchment covers so that 

 the cylinders freely communicate with 

 each other, a very fair idea will be 

 gained of a sieve-tube : the perforated 

 parchment covers will, of course, 

 answer to the sieve-plates. These 

 vessels retain their protoplasm, which 

 circulates through the sieve-plates, 

 and they evidently play an important 

 part in the life-history of the plant. 

 The German physiologist, Sachs, was 

 of opinion that much of the new 

 protoplasm is produced in the sieve- 

 tube, and this view is shared by Pro- 

 fessor Thome and other eminent 

 botanists. These also are the vessels 

 which play so important a part in the 

 diffusion of the sugar formed by the 

 chloroplasts in the leaves of plants. 



In the leaves and outer bark of 

 many plants, thin-walled vessels of 

 various structure may be met with, 

 which usually run parallel with each 

 other and invariably contain bundles 

 of needle-shaped crystals. These are 

 closely related to the sieve-tubes, and 

 are known as utricular vessels. A very 

 large number of plants have them.* 



The laticiferous vessels, which may 

 next engage us, though of much 

 interest from a physiological point of 

 view, need not detain us long. These 

 vessels, as their name implies, convey 

 the milk-sap or latex to the parts of 

 the plants which require, or, at least, 

 seem to require it : for there is some 

 doubt as to the function of latex 

 whether it is more than a by-product. 



* According to Professor Thome (Lehrbuch, 

 p. 32), they occur in most Monocotyledons, and 

 ! n S me Dicotyledons being found exclusively 

 in the outer cortex or the foliar organs. 



