SUPPLEMENT 93 



so small that careful searching is necessary to determine their presence. Such 

 extreme cases appear certainly to be hereditarily fixed (habitual anisophylly), 

 while less striking cases are conditioned by external factors, among which the 

 direction of light is frequently one which plays a prominent part (NORDHAUSEN, 

 1901 ; FIGDOR, 1904). 



I. 14, after darkness read (SACHS, 1864 ; WIESNER, 1893). 



II. 17-21, for The formation of ... in red light.] read The influence of the 

 quality of the light on the pigments of plants is of especial interest. The forma- 

 tion of chlorophyll, as REINKE (1893) has shown, can take place in light of all 

 wave lengths between FRAUNHOFER'S lines A and H, but those between B and D 

 are the most effective. Not all pigments, however, behave in this way ; 

 GAIDUKOW has recently made some very interesting statements as to the pig- 

 ments which accompany chlorophyll in certain Algae. Several Algae have the 

 capacity of showing chromatic adaptation by developing in their chloroplasts 

 pigments which are complementary to the colour of the light which falls on 

 them. Thus he has shown (1906) that a blue-green alga (Phormidium tenue) 

 changed its colour to yellow-brown in the course of a few hours after being ex- 

 posed to the more refrangible rays of electric light passed through a spectro- 

 scope, but that it remained blue-green when exposed to red rays. In similar 

 experiments the red alga (Porphyra) took on a green colour where exposed to red 

 and yellow rays. In consequence of the great importance of this discovery as 

 regards the problem as to the relation between the colour of light and assimila- 

 tion, it is highly desirable that GAIDUKOW should discuss certain pertinent 

 criticisms which may be made on his observations ; more especially he must tell 

 us how these chromatically adapted cells behave later on whether they do not 

 die off as a result of this change in colour . 



Rays beyond the visible part of the spectrum also have an effect on plant 

 form. 



313, 1. i, for the accessible . . . shown by read the effects of gravity 

 accessible to 



1. 20, before increasing read moderately 



1. 22, for (MoxxiER, 1899) . . . expected read and an interruption of 

 growth also takes place (ANDREWS, 1902). 



1. 32, after (anisophylly). read Gravity is more concerned in anisophylly 

 than light. 



I. 47, for develop progressively . . . normal read spread further towards 

 the opposite pole than when in the normal 



314, 11. 13-15, for Growth in thickness . . . the under read Further, tissue 

 formation takes place unequally as a consequence of the unilateral influence of 

 gravity. In branches whose full-grown regions are placed obliquely, scleren- 

 chyma and vessels on the upper side develop narrow lumina and thick walls, 

 those on the under side wide lumina and thin walls (BucHER, 1906). Secondary 

 thickening in such sloped branches is also eccentric. 



II. 22-4, for gravity. Further . . . HARTIG read gravity (comp., how- 

 ever, URSPRUNG, 1905, 1906). Further, the under side is distinguished not only 

 by more vigorous growth in thickness, but also by a definite histological struc- 

 ture, and by special mechanical characters in the wood formed (SONNTAG, 1904). 

 This wood, spoken of from its colour as ' red wood ', is highly resistant to 

 pressure, but its power of resisting tension is only half as great as that of the 

 so-called ' white wood ' formed on the upper side of the branch. Since the 

 upper side is, for the most part, subjected to tension, and the under side to 

 pressure, the object in forming these tissues is apparent. In all probability 

 (EwART, 1906 ; HARTIG, 1901) this formation of different kinds of secondary 



