132 PHARMACEUTICAL BOTANY 



Abnormal Structure of Dicotyl Roots. In certain Dictoyl roots 

 as Amaranthus, Jalap, Pareira, and Phytolacca, after the normal 

 bundle system has been formed, there then develop successive cam- 

 biums outside of these bundles, producing concentric series of open 

 collateral bundles. 



Histology of a Dicotyl Tuberous Root (Aconitum). A transverse 

 section made through the tuberous root of Aconitum Napellus near 

 its middle shows a cork region of one or more layers of blackish or 

 brownish cells; a broad cortex of two regions, viz.: an outer narrower 

 and an inner broader zone. The narrower zone consists of from 

 eight to fifteen layers of cortical parenchyma cells, interspersed among 

 which are numerous irregular-shaped stone cells. Separating this 

 zone from the broader one is an endodermis of a single layer of tan- 

 genitally elongated endodermal cells. The broader zone consists of 

 about twenty layers of parenchyme cells. Next, a five- to seven- 

 angled cambium, within the angles of which and frequently scattered 

 along the entire cambial line, occur collateral fibro-vascular bundles. 

 In the center is found a broad five- to seven-rayed pith composed of 

 parenchyma cells. The parenchyma cells of the cortical regions and 

 pith contain single or two- to five-compound starch grains. 



ROOT TUBERCLES 



The roots of plants of the Leguminosa, Myricacece as well as some 

 species of Aristolochiacece and of the genera Alnus and Ceanothus are 

 characterized by the appearance upon them of nodule-like swellings 

 called root tubercles. In the case of the Leguminosce the causative 

 factor is a species of bacteria named Pseudomonas radicicola. This 

 is a motile rod-shaped organism which appears widely distributed 

 in soils. It is apparently attracted to the root-hairs of leguminous 

 plants by a chemo tactic influence probably due to the secretions 

 poured out by these structures. A number of these organisms pene- 

 trate the walls of the root-hairs by enzymic action. Upon entering 

 the hairs they form bacterial tubes which branch and rebranch and 

 extend into the middle cortex cells carrying the bacteria with them. 

 Within the cortex cells the organisms multiply rapidly producing 

 nest-like aggregations. Their presence here causes the formation of 

 nodules or tubercles. Under oil-immersion magnification these 



