ELISHA MITCHP:LL SCIENTIFIC SOCIETY. 115 



ments on tlie roots I expected to find Plasmodiophora Bassicce, 

 until after I had made the microscopic examination and found 

 the cause to be a worm. Perhaps the enlargements of "club- 

 foot," before they begin to crack, are a little more even in con- 

 tour than those of root-galls, and in the specimens I have seen 

 those of '^club-foot" are larger, especially on the tap root, where 

 very large lateral growths are formed. But if we take a thin 

 transverse section of an enlarged root of each and compare them 

 all resemblance vanishes. In a cross section of '^club-foot" the 

 first thing to attract attention is the great number of yellowish 

 Plasmodia, or else the spore masses within large cells, distributed 

 all through the tissues. If the section is from an enlargement 

 of a lateral root, unless very large, there will be little else to 

 attract the attention when compared with a healthy root, unless 

 it be a slight enlargement of some of the other cells. The gen- 

 eral character of the root structure is but little changed The 

 tracheal tissue of the axis cylinder, but little attacked, is arranged 

 in the same stellate form which we find it in a healthy root. 

 The ducts, even when immediatelv in contact with cells contain- 

 ing Plasmodia, are not turned from their longitudinal direction, 

 or if sn, only slightly. The cells are not elongated and curved 

 around the enlarged cells containing the plasmodium, but resem- 

 ble the normal arrangement of small cells around a large one. 

 Nor is the radial diameter of the parenchymatous cells propor- 

 tionately increased, but if the cells are enlarged it is usually a 

 proportionate or nearly symmetrical enlargement. In this sec- 

 tion from the root-gall here and there is a cyst, or the amorphic 

 remains of one containing eggs and larvse. The color is not so 

 yellowish as that of the plasmodia nor are the cysts so numerous. 

 Indeed the most striking feature in the appearance of the cross 

 section is the twisted, curved and distorted condition of the cells, 

 especially of the tracheal vessels. In some places these are beau- 

 tifully wreathed about a cyst, and by their side run very much 

 elongated j)arenchyma cells, while in another place a labyrinth 

 of vessels is woven with the parenchymatous tissue, giving to the 

 section as a whole, viewed with the compound microscope, the 



