ZOOLOaX AND BOTANY, MICROSCOPY, ETC. 867 



furnisli the seedling plant, during the early stages of its development, 

 with the carbohydrates necessary for the formation of its cells. The 

 quantity of hydrocyanic acid produced in germination is, however, 

 very small ; large quantities would have a poisonous effect on the 

 growing plant. 



Galvanic Phenomena in Germinating Seeds.* — J. Miiller- 

 Hettlinger has investigated the electrical phenomena presented by 

 the apex of the roots of germinating seeds, especially of Vicia Faba, 

 Zea Mays, and Biota orientalis, from the time of the protrusion of the 

 radicle through the testa to the appearance of the first foliage-leaves. 

 In the case of all these plants, and in all stages of development, the 

 galvanometer indicated a current from the cotyledons and the radicle, 

 caused by the electronegative condition of the latter and the electro- 

 positive condition of the former. But every point of the root, and 

 also of the secondary roots when they had made their appearance, 

 and every point of the first foliage-leaves, and especially of the 

 tigellum, was electronegative in relation to the cotyledons, but with 

 decreasing intensity the nearer it was to them. The following law 

 could therefore be formulated : — If one of the conducting electrodes 

 is imagined constantly placed at the cotyledons, while with the other 

 the current is successively conducted from the other parts of the 

 seedling above and below the cotyledons, an electromotor force is 

 always set up, caused by the electropositive condition of the testa 

 or cotyledons contrasted with the electronegative condition of all the 

 other parts of the seedling ; and this force is less intense the nearer 

 the movable electrode is to the cotyledons whether above or below 

 them. 



Mechanical Protection of Seeds against External Injury.f — In 

 respect to peculiarities under this head, K. Marloth classifies seeds 

 into five groups, as follows : — 



1. Those seeds in which the testa has no protective contrivance • 

 the endosperm is wanting, or is only rudimentary. The number of 

 plants belonging to this group is small ; their very small seeds are 

 dispersed by the wind and germinate in damp places. 



2. Protective contrivances are also wanting, or are only very feebly 

 developed ; but the endosperm is abundant, consisting of thick-walled 

 cells, and serves as a protection to the embryo which it incloses. In 

 some the outer wall of the epidermis is thickened. In some which 

 bear berries, the endosperm protects the embryo in its passage through 

 the body of birds. 



3. The testa has protective contrivances, and the endosperm is 

 wanting or is only feebly developed. A very large group in which 

 the protective layers are developed in a great variety of ways : — as 

 simple thickenings of the epidermis, a deeper layer of thickened cells, 

 a simple layer of thick-walled parenchyma, palisade-cells, lignified 

 parenchyma, sclerenchyma, and a development of prosenchyma. 



* Pfluger's Arch. f. Phys., xsxi. p. 193, See Naturforscher, xvi. (ISSS) 

 p. 235. 



t Engler's Bot. Jahrbiicher, iv. (1883) p. 225. See Naturforscher, xvi. C1883) 

 p. 349. 



