30 Introduction to Botany. 



cells, end to end, which extend continuously through the 

 stem into the leaves, where they branch and help to form 

 the veins and veinlets. Make similar sections of a root, not 

 more than three millimeters in diameter, of some woody 

 plant, and treat with phloroglucin as before. The ele- 

 ments, which in this instance are colored red, consist of 

 wood fibers in addition to the water-conducting tubes. The 

 larger openings of the latter can easily be seen by means 

 of a simple lens. 



47. Make a cross section of a small sweet potato, which 

 is in reality a root, and treat with the iodine solution. The 

 section is stained purple, because it is filled with starch 

 which supplies with food the young shoots that spring 

 adventitiously from the root. Plant some sweet potatoes 

 in moist sand and keep in a warm place. As the shoots 

 develop, what change is noticed in the size of the root.? 



48. Make cross sections of dodder, which is parasitic on 

 balsam, stinging nettle, or some other herbaceous plant. 

 This material gives best results if it is taken in a young 

 and tender condition and placed in 70 ^ alcohol for a time, 

 and afterwards preserved in equal parts of alcohol, glycer- 

 ine, and water. Or it may be kept from the first in a 2 ^ 

 formalin solution. Select a section showing the penetra- 

 tion of the roots of the dodder into the host plant. Treat 

 first with phloroglucin and then mount in chlor-zinc-iodide 

 (see page 381), or mount in the latter reagent alone, and 

 examine with the compound microscope. An examination 

 with a simple lens even will give a fairly good idea of the 

 intimate relation between the parasite and its host. 



49. Take germinating seeds of Indian corn whose 

 primary roots are about one centimeter long, and with 

 waterproof India ink make marks on the roots one milli- 

 meter apart, beginning at the apices. On other roots 



