ZOOLOGY AND BOTANY, MICEOSCOPX", ETC. 297 



anatomical structure of the tricotyledonous embryo in a variety of 

 Phaseolus vulgaris in which it is very frequent. 



Tricotyledony is hereditary in various degrees, but there is always 

 a tendency to reversion to the normal condition. The ternary arrange- 

 ment characterises the whole anatomical structure in tricotyledonous 

 seedlings ; but there are intermediate forms between the binary and 

 ternary arraugenients. The third cotyledon of tricotyledonary seedlings 

 may be inserted on the dorsal or on the ventral face of the hypocotyl, or 

 it may be placed unsymmetrically. Its insertion may be a little above 

 the zone of insertion of the two normal cotyledons, or the three may con- 

 stitute a true whorl ; the position of the supplementary cotyledon deter- 

 mining the anatomical structure. The special anatomical characters of 

 tricotyledonous seedlings are exhibited in the root, the hypocotyl, the 

 epicotyl, and the first whorl of leaves. 



Perfect tricotyledony was not observed in Phaseolus. Even when 

 the external form was completely symmetrical, the three regions of the 

 ternary structure were not identical. The anomalous number of 

 cotyledons bas a tendency to produce other anomalies also in the young 

 plant. 



The observations of the author tend to confirm the importance of 

 the number of cotyledons as a starting-point in classification. 



Root-Tubercles of the Leguminosse. * — L. Hiltner discusses at 

 length the causes which determine the size, number, position, and action 

 of the root-tubercles of the Leguminosse, with special reference to the 

 culture experiments carried out at Tharandt. The roots of Leguminosaa 

 exude certain substances which have an attractive power over bacteria ; 

 while, on the other hand, the tubercle-bacteria form " attacking sub- 

 stances " (An griff sstoffe) on the roots of the Legunrinosse, causing the 

 cell-walls of the root-hairs to swell up without becoming completely 

 disorganised. The author draws from the results of these experiments 

 the conclusion that the tubercle-bacteria of various species of Leguminosse,. 

 while differing from one another in their physiological properties, are, 

 for the most part, morphologically identical. The bacteria of Pisum 

 and Bobinia cannot, however, be made to replace one another. 



With regard to the infection of individuals already furnished with 

 tubercles, the author lays down the general law that active tubercles 

 endow the plant with immunity against bacteria of the same or of an 

 inferior degree of virulence as compared to those already present in the 

 tubercles ; only bacteria of a higher virulence can enter the tubercles. 

 The statement often made that the tubercles are always formed as near 

 to the surface as possible is erroneous. 



Root-Tubercles of Medicago sativa.j — According to observations of 

 N. Passerini the roots of the lucerne have abundant root-tubercles during 

 the first year of cultivation ; very few during the second, and none at 

 all in the third. He infers that the plant makes use of the atmospheric 

 nitrogen obtained through the tubercle bacteria only during its first 

 year, until the roots have attained sufficient length to obtain the necessary 

 nitrogenous food-materials from the deeper soil. 



• Arb. Biol. Abth. k. GesundhMtsamte, Heft 2 (1 pi.). Sue Bot. Centruli>l., 

 lxxxv. (1901) p. 179. f Bull. Soc. Bot. Ital., 1900, pp. 16-7. 



