CHAPTER IX. 

 DICOTYLEDENOUS ANGIOSPERMS 



INDIAN TOBACCO (Lobelia inflata) 



Habitat. Indian tobacco is abundant in fields and 

 meadows where the growth is not over rank. 



Morphology. The plant, which is annual, is clearly differ- 

 entiated into roots, stems, branches, leaves, flowers, fruits 

 and seeds. The roots, which are all branches of a primary 

 root, have the tissues differentiated into a cortical region 

 separated from a wood region by the cambium zone which, 

 in the perennial woody dicotyledons, forms cortex on its 

 outer face and wood upon its inner face, thus adding to the 

 diameter of the root from year to year. On the younger 

 portion of the young roots there is a root hair region which 

 develops as the rootlets increase in length and disappears 

 when the epidermis is replaced by the periderm or corky 

 outer layer. 



The stems are usually much branched and are covered 

 with hairs. The stem, like the root has a cortical, cambium, 

 wood and pith region. Because of these facts the whole group 

 is known as exogenous plants because the fibro vascular tissue 

 is open and is arranged in a circle and surrounded by a cam- 

 bium as in the 'roots, which in perennial dicotyledons adds 

 new cells to the wood and cortex, thus making it possible 

 for the plants to yearly increase their diameter. The vessels 

 in the wood are tubes, frequently of great length, and through 

 which water and cell sap readily pass. Trees and shrubs in 



