ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1 ( J3 



conditions. As a rule the light-stimulus increases as the amount of 

 light decreases. In uniform light and temperature the movements do 

 not cease at once, but gradually, the rhythm being similar, but the 

 amplitude decreasing. Some plants, e.g. Mimosa and Albizzia, have a 

 very rapid time reaction, while others, e.g. Phaseolus, only respond 

 after a considerable period. The two former genera are affected both 

 by increase and decrease of light, while the latter is only affected by 

 the increase of light in the morning. In plants like Phaseolus, which 

 have a long reaction time, the process of stimulation continues for some 

 time after the cause of the stimulus has ceased. Flowers which exhibit 

 sleep-movements behave in the same way as foliage-leaves, e.g. the tulip 

 and crocus behave like Mimosa, and flowers with slow time reactions 

 behave like Phaseolus. In general, plants which respond to changes in 

 temperature will also respond to changes in light, the same movements 

 being produced by change in either condition. 



CRYPTOGAMS. 



Pteridophyta. 

 (By A. Gepp, M.A., F.L.S.) 



Root-structure in Ceratopteris thalictroides.* — A posthumous 

 paper by P. Lachmann has been published, on the origin and develop- 

 ment of the roots and rootlets of Ceratopteris thalictroides. The subject 

 is treated of fully under three heads : (1) Origin of the roots ; (2) 

 Development of the root ; (3) Origin and Development of the rootlets ; 

 and a resume is given at the conclusion of each part. The author finds 

 that the first ten or twelve roots of Ceratopteris emanate from the stem, 

 while the later ones proceed from the leaves, where they occupy the 

 basal region of the petiole. As regards the development of the root, the 

 mother-cell produces groups of elements, usually composed of one 

 rootcap-segment and of three series of cortico-stelic segments. These 

 are all described in detail. The centre of the stele is occupied by large 

 cells or potential vessels which, in most ferns having a binary root, are 

 differentiated into large scalariform vessels and consequently do not form 

 a pith. The formation of the tissues composing the central cylinder is 

 clearly centrifugal, while their differentiation is centripetal. 



A study of the rootlets of Ceratopteris shows that they are disposed 

 in two rows diametrically opposite and produced by two series of sextants, 

 predestinated for their formation and for that of the ligneous bundles. 

 The division of each of these sextants is described. The apex of the 

 rootlet frees itself by piercing the piliferous layer of the root-mother. 

 The author has never seen the intra-lacunary rootlets described by 

 Poirault. From the very base the rootlet possesses its piliferous layer 

 and two quite distinct cortical zones ; consequently, there is no epistele. 

 The connection of its conducting tissue with that of the root is 

 established across the pericycle of the latter, without the production of a 

 " pedicule pericyclique " analogous to that described by Van Tieghem 

 and Douliot for other species. The paper is illustrated by thirty-seven 



figures. 



* Rev. Gen. Bot., xix. (1907) pp. 523-56 (figs, in text). 



