INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 479 



silver firs (Abies of Continental, Picea of British writers), and the 

 spruce firs {Picea of Continental, Abies of Britisli writers). In those 

 silver firs in which the leaves are so crowded as to overlap each other 

 closely, and where their relatively flat surfaces permit only one face 

 at a time to be exposed to the light, not only are the leaves twisted so 

 as to bring them all into nearly the same plane, but they are in many 

 cases, if not in all, endowed with a power of alternate elevation and 

 depression, so that the lower surface may be exposed at times to the light. 

 In spruce firs, as a rule, the leaves are less densely packed than is the 

 case with the silvers, and they are usually more or less four-sided. 

 There is torsion at the base of the leaf, but ajiiiarently little or no 

 motion of elevation or depression. The so-called " palisade-cells " 

 are nearly confined to the ujiper surface of the flat-leaved silver firs, 

 and are apparently connected with their singular power of elevation 

 and depression. 



Relationship between Light and Etiolin.*— The term etiolin has 

 been given by Pringsheira to the yellow pigment which colours the 

 amorphous or granular protoplasm found in the seedlings of Angio- 

 sperms in the dark. Its relationship to liglit has been investigated 

 by Elfving, who for this puri)ose exposed etiolated seedlings for a 

 short time to light, comijaring the results with others kei)t in the dark. 

 He states that the yellow colour is produced only by the less re- 

 frangible rays of liglit. It cannot be asserted that absolutely no 

 etiolin is produced by blue and violet light ; but it may be stated with 

 certainty that the less refrangible rays are much less efficacious in its 

 formation than the more refrangible ; as is indeed also the case with 

 other chemical processes in the plant dependent on light. 



Growth of Negatively Heliotropic Roots in the Light and in 

 the Dark.f — The accepted explanation of lieliotropic cuiwature, first 

 proposed by A. P. Do Candolle, is that growth in length is promoted 

 by dark and hindered by light, and that in consequence a growing 

 organ such as an iutoruode, exposed to light on one side, will curve 

 towards the source of light. If this theory is correct, negatively 

 heliotropic organs should grow more rajjidly in the light than in tho 

 dark, a result not in accordance with the observations of Schmitz and 

 Mailer (of Thurgau). 



F. Darwin has, in order to test the correctness of this hypothesis, 

 watched the growth of the negatively heliotfopic roots of seedlings of 

 Sinapis (dha ; and the result of his observations determines with cer- 

 tttuity that at all events some negatively heliotropic organs may grow 

 faster in the dark than in light. The author is here led to agree with 

 the conclusion arrived at by Sachs, that hcliotropism, like geotropism, 

 is a phenomenon of irritation, and that Do CandoUe's theory is not 

 supportf'd by facts. 



Chlorophyll in the Epidermis of the Leaves of Phanerogams.!— 

 It bus been commonly stated that chloropliyll is absent from tho 



* 'Arbeit. Rot. Inst. Wiirzhurg," ii. (18S0) p. -IDS. f Ibifl., p. .')21. 



X * Sl{. Akii.l. \Vi.>s.' (Wion). Ixxix. (IK7;») iHf Sec, p. ST. 



