ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 75 



moist and a drier medium, to direct themselves towards the former, to 

 an extent often sufficient to overbalance geotropism. As the resul' of 

 a series of observations, M. Mer contests the view that hydrotropism 's 

 a special instinctive faculty of the root ; he attributes the phenomeno 

 to the retardation of growth consequent on an insufficient supply of 

 moisture, a condition which may completely prevent the manifestation 

 of geotropism. 



Cause of the Swelling of Root-fibres.* — E. Mer and M. Cornu 

 have observed that when the roots of growing plants are placed in 

 coloured fluids, if the solution is too concentrated so as to check 

 growth, each root-fibre swells near the apex, the swelling being often 

 accompanied by a more or less decided curvature. M. Cornu attri- 

 butes this phenomenon to the same cause as the swellings caused by 

 phylloxera and by gall-insects, viz. not the special influence of a 

 particular fluid, but tensions developed locally by any cause, and in 

 many cases the arrest of development of an organ in course of 

 elongation ; the production of a fluid may, however, in certain cases 

 co-operate with this. 



Frank's Diseases of Plants. — The completion of this work, to 

 the publication of the 1st part of which we have already alluded,| 

 furnishes a very complete account of the various diseases and injuries 

 to which plants are subject. It is divided into five sections, as 

 follows : — 1. The living and dead state of the vegetable cell. 2. 

 Action of mechanical influences. 3. Diseases caused by influences of 

 inorganic nature. 4. Diseases caused by other plants. 5. Diseases 

 caused by animals. 



Under the first head the author describes the phenomenon known 

 as the " apostrophe " of the chlorophyll-grains. The normal position 

 of the chlorophyll-grains he states to be in a layer especially next to 

 those parts of the cell- wall which are not in contact with adjacent 

 cells — on the outer side, therefore, of epidermal cells, and on walls 

 that border intercellular spaces ; and to this position he applies the 

 term epistrojphe. Certain unfavourable influences, as long-continued 

 absence of light, wounds, &c., cause the chlorophyll-grains to lose 

 this position, and group themselves along those cell-walls that are 

 in contact with other cells ; and this abnormal position he calls 

 apostrophe. 



The production of wens is thus described. The first cause is 

 always a small wound in the periderm, which sometimes appears to be 

 a crevice over a lenticel. Between the dried margins of the outer 

 ruptured cortical layer there then projects a living new formation in 

 the form of a light-brown cushion, which is either a round tuber or a 

 long wheal, according to the shape of the wound ; a cluster of smaller 

 tubers often break out in addition from the bottom of the wound. 

 When this cushion projects to a height of 1 mm. above the wound, 

 it consists only of cortex and bast, not of wood ; it is a hypertrophe 

 of the cortex, enclosed in a young periderm. The parenchymatous 



* Bull. Soc. Bot. France, xxviii. (1881) pp. 12i-7. 

 t See this Journal, i. (1881) p. 273. 



