74 PRACTICAL BOTANY 



lateral, horizontal branches frequently connect the parallel 

 tubes. 



With a high power make out more accurately the course of 

 a group of the vessels. 



II. Cut transverse sections of the same ; mount in glycerine, 

 and examine with a low power. 



The laticiferous vessels appear circular in transverse section, 

 and have brown contents : they are distributed in groups, which 

 form more or less regular concentric rings round the central 

 xylem. They may be recognized still more distinctly in sections 

 stained with alkannin, or with potassium bichromate. 



Note in these sections the presence of sphere-crystals of 

 inulin : in the former section they will have been dissolved 

 by the treatment with potash. Observe that they are formed 

 quite irrespective of the cell-walls, which are often included 

 in them. 



ii. Laticiferous Cells. 



I. Cut tangential sections of the cortex of Euphorbia 

 splendens (other species will do) just outside the vascular ring, 

 and mount in water, or dilute glycerine : or stain with alkannin, 

 and mount in glycerine. 



Examine with a low power. 



Running through the cortical parenchyma will be seen long 

 tubes, with thick cellulose walls and granular contents. These 

 are the laticiferous cells, which differ from the preceding in 

 being developed, not by fusion of originally distinct cells, but 

 by continued apical growth of single cells. 



Note cases of branching of these cells. 



Included in the granular contents are starch-grains of 

 pecular dumb-bell form. 



Treat sections with iodine solution, and observe the effect on 

 these bodies. 



I.I. Cut transverse sections of the same stem, and note the 

 distribution of the laticiferous cells ; they may be recognized by 

 their walls, which are thicker than those of the surrounding 

 tissues, and appear circular in section. 



