56 GROWTH AND WORK OF PLANTS 



The uncoiled spiral is strong enough to support by suspension a 

 piece of the stem 2 cm. to 4 cm. long, and so delicate that one 

 cannot see the means of support at a little distance unless held 

 before a black object or the light. Examined under the micro- 

 scope the beautiful spiral markings can be seen. 



STRUCTURE OF THE STEM OF DICOTYLEDONS. 



96. Gross structure of the stem of an annual. A cross 

 section of the stem of a dicotyledon shows a very different 

 structure (fig. 51, A). Leafy shoots of dicotyledonous stems like 

 the garden balsam or touch-me-not (Impatiens), bean, sun- 

 flower, etc., may be placed with the cut ends in red ink or a 

 solution of a red analin dye. After several hours the loss of 

 water from the leaf will draw the colored liquid up through the 



Fig. 56. 



Xylem portion of bundle. Cambium portion of bundle. Bast portion of bundle. Section 

 of vascular bundle of sunflower stem. 



vascular ducts. This will stain the bundles, and also the veins 

 of the leaves in many cases, so that the color is easily seen through 

 the thin overlapping tissues. If shoots with white flowers are 

 also placed in the dye the white petals will become stained. If 

 the stems are now cut across the position of the bundles can 

 be seen. Instead of being scattered without order through the 



