915 



Although the iininber, position, size, form, etc., varied in the case 

 (►f ditt'erent s])e<'ies of plants, the anatomy of the tubercles was found 

 practieally the saiiH' for all, and was very ditterent from that of the 

 roots liearinii' them. The author's descri])tion of the structure of the 

 tubercles was briefly as follows: The tuben-les consist of an outer 

 layer of bark parenchyma, often containing starch, inclosing- an inner 

 tissue of circular cells which increase in size as the center of the tuber- 

 cle is approached. IJetween the two kiiuls of tissue are a number of 

 tibro vascular bundles, which are branches of those in the root but do 

 not proceed to the end of the tubercle. The central tissue contains a 

 thick, cloudy layer of i)roto])lasm on its inner walls, sometimes com- 

 pletely tilling the cells. This cloudiness is attributed to iniuimerable 

 small, elongated, rod shaped bodies, usually consisting of two or three 

 small branches, and resembling vibriones. They are stained brownish 

 green by iodine, like i)rotein substances, and exhibit a lively mofecular 

 and sometimes a vibrio motion in water. 



The tubercles are transitory, seldom lasting through the year, and 

 are continually being formed during the greater part of the life of the 

 plant. They are decomposed by a peculiar process of solution, and at 

 the same time new tubercles are formed on the younger branches ot 

 the roots. lie believes the tubercles to be of physiological rather than 

 pathological nature. They possess an unusual capacity for absorbing 

 li(juids, but he doubts whether their function consists exclusively in 

 furnishing the plant with Avater. Regarding their true function he seems 

 to be somewhat in doubt. He refers to the general belief anumg farmers 

 that certain leafy itlants, notably i)apilionaceous plants, are able to 

 assinulate the free nitrogen of the atmos])here. lie intimates that these 

 root tubercles may have a connection with this supposed ability. He sug- 

 gests that by their means leguminous ])lants may be able to use to better 

 advantage and more comi)letely than otlier plants the nitrogen applied to 

 the soil in the form of ammonium salts or nitrates, in that the tubercles 

 act as reservoirs for collecting and storing nitrogenous materials which 

 later can be given up to the plant as it recpiires. The supply of ammo- 

 nium salts and nitrates in the soil may be cut oft' from the reach of 

 plants with short roots by being waslied into the lower layers of the 

 soil by rains. In that case the i)apili()i!ai'eous plants can fall back upon 

 the reserve i)rotein substances stored up in the tubercles and thus 

 continue their growth. If the papilionaceous plants do enrich the 

 soil with nitrogen, as agriculturists claim, then this, he says, is prob- 

 ably due to the richness of their roots, and ]iarticularly the tubercles, 

 in nitrogenous compounds. The latter are in a sense reservoirs storing 

 u]) plant food, especially nitrogen, at favorable times when an excess is 

 available, and preventing it from l)eing washed away from the reach of 

 the roots. Later their su^tply of plant food is given up to the jjlant or 

 the soil. 



