122 EXPERIMENT STATION RECORD. 



ating the micro-organism witliout injury to the nucleus, although in Ornithopus the 

 nucleus was somewhat enlarged. 



The root tubercles of bur clover and of some otber leguminous plants, 

 Ci. J. I'EincE {Pror. California Acad. Sc.L, 3. ser., Bol., 2 {1902), No. 10, ])p. 295-328, 

 pi. 1). — While examining some sections of root tubercles of the bur clover {Medicago 

 denticulata), the author was struck by the great difference between cells containing 

 bacteria and those in which there were none. This led to a careful microscopic study 

 of the root tubercles of the bur clover and other leguminous plants to ascertain 

 if possible the real relations of the tubercular organisms to the cells in which they 

 are found. After describing in detail the method of procedure, the author considers 

 the origin and morphology of the root tubercles, their form, distribution, and 

 structure. 



Summarizing his results, the author found that bacteria wdiich form root tubercles 

 on leguminous plants are usually slowly motile in artificial cultures, although this 

 proves nothing for their movement through the soil. The proportion of root hairs 

 affected in the case of the bur clover was about 1 :1,000. If the bacteria are in contact 

 or close proximity with the young root hairs many infections may occur simulta- 

 neously. The root tubercle liacteria enter and infect a root hair by softening or dis- 

 solving a portion of the cell wall. There is no evidence whatever that they enter 

 through l)roken root hairs. The infection thread grows fairly straight through the 

 cortical ])arenchyma from the root hair to the layer of cells next the outside of the 

 central cylinder of the root. Tubercles are formed only as a result of the stimulating 

 action of the bacteria, and are originated endogenously from the same layer as that 

 which gives rise to lateral roots, hence morphologically they are lateral roots greatly 

 modified by the influence which caused their formation. The growth of the root 

 tubercle is apical and there is little if any secondary growth in thickness. Root 

 tubercles are usually largest and most numerous near the surface of the soil, and it 

 is probaV)le that perennial leguminous plants form few if any tubercles after their 

 roots have penetrated deeply into the soil. 



The presence of bacteria in the cells of a tubercle prevents those cells from forming 

 starch. The affected cells are usually larger than normal ones, due to the increased 

 pressure and to the greater irritation. The l)acteria cause the degeneration and almost 

 complete destruction of the nuclei of the cells in which they occur. The infection 

 strands grow definitely toward the daughter cells formed by the meristem, and seem 

 to grow toward the nuclei, which they appear to penetrate. Infected cells soon lose 

 their power of division, but not of growth. The presence of the bacteria in the cells 

 of the tubercle is injurious to the cells, the relation l)eing one of true parasitism on 

 the part of the bacteria. The presence of intercellular spaces in the root makes it 

 unnecessary to assume that the bacteria live anaerobically, as has been assumed by 

 some investigators. 



In conclusion, the author states that it is difficult to understand how the legumi- 

 nous plant as a whole can profit by an association which is injurious and finally 

 destructive to the cells in which the bacteria occur. 



On the development of root tubercles of leguminous plants, E. Laurent 

 {Compt. Rend. Acad. Sci. Paris, 133 {1901), No. 26, pp. 1241-1243; rqmnted in Prog. 

 Agr. et Vil. {Ed. L'Est), 23 {1902), No. 13, pp. 387, J<?<?).— Since 1897 the author has 

 been studying the effect of certain fertilizers on the production of root tubercles upon 

 the roots of leguminous plants. The i)lats have each year received the same fertilizer 

 and have been grown with the same crop successively. One plat was manured with 

 a nitrogenous fertilizer, a second with potash, a third with superphosphate, a fourth 

 with lime, and a fifth with sodium chlorid. The plants experimented with were 

 peas, hairy vetch, common vetches, and lupines. One object of the experiments was 

 to determine whether by continuous cultivation under similar conditions the plants 

 would acquire characteristics resistant to parasites or other biological changes. In 



