MacDougcd: nitrogen assimilation. 41 



groups, is developed in the form oi radial wedge-shaped ex- 

 tensions reaching half the distance to the corky layer. To a 

 marked development of the parenchyma surrounding the central 

 cylinder is due the size of the tubercle. The corky layer is 

 strongly developed in mature tubercles, but apparently retains 

 its power of growth during the entire life of the tubercle. Pro- 

 fessor C. W. Hargitt read a note od the structure of the tubers, 

 before the American Association for the Advancement of Sci- 

 ence, at Indianapolis, in 1890, which was afterward published -, 

 and the results of his work are not entirely confirmed by the 

 observations recorded here. 



Numerous examinations, with a view to determining the 

 chemical nature of the cell contents of the tubers, have been 

 made in the laboratories of the De Pauw and Purdue univers- 

 ities, and at the University of Minnesota. Such examinations 

 show uniformly an entire absence of starch, and sugar in its 

 ordinary forms. The presence of inulin is noted by Professor 

 Hargitt, but, although all known tests were made for this sub- 

 stance, including Green's ^ using alcohol, orcin or phloro- 

 glucin and hydrochloric acid, yet not even a trace of this sub- 

 stance could be detected. As a control the reagents were 

 tested on the tubers of Syndesmon thalictroides (Anemonella), 

 which contain large quantities of inulin. In the parenchyma 

 tons tissue and inner layers of the cork of the Isopyrum tuber 

 are large numbers of bodies which give some of the reactions 

 of protein globoids together with others of a fatty or waxy na- 

 ture. Intermingled with these bodies are numerous organisms 

 of a bacterial nature whose morphology is yet undetermined. 

 The infection of the root by these organisms takes place before 

 the corky layer is strongly developed, and since the formation 

 of the tuber begins before the secondary thickening of the 

 root, it is surmised that the extraordinary growth of the 

 cambium and parenchyma is due to their irritant action. A 

 number of healthy plants, which had begun a second groVth 

 of the stems, were received from Dr. L. M. Underwood, of 

 Greencastle. Indiana, October 31, 1893, and were immediately 

 placed in pots in the plant house. The condition of the tubers 

 was noted at the time, and two weeks later, when the stems 

 and leaves were strongly developed, a second examination re- 

 vealed the fact that the tubers, instead of showing a shrinkage, 

 had actually increased in size at a time when the plant was to 



2. Hartfitt, C. W. Bntanical Gazette 15 : 235. 1890 



3. Green. Ann. B»t. 1 : 233. 1S88. 



