INFLUENCE OF EXTERNAL STIMULI. LIGHT 251 



not pectinated ; their surface is then not placed at right angles to the 

 incident light rays, but they are all more or less upright in the direction 

 of the dorsal surface of the shoot, and those which stand upon the dorsal 

 surface itself show in consequence not infrequently wax-striae upon their 

 upper side, but these are not so strongly developed as are those upon 

 their under side. Anisophylly then appears here also, but it is not so 

 striking as in the first-mentioned case, and without measurement is scarcely 

 recognizable. Some examples of measurements of needles chosen at 

 random may be given, a being dorsally placed ones, and b ventrally 



placed ones, 



a b 



19 mm. 22 mm. 



16 mm. 21 mm. 



Sometimes the differences are greater, sometimes they are smaller. The 

 relations of the dorsiventrality to illumination are also here instructive ; 

 the smallness of the dorsally placed needles is perhaps so far of benefit 

 as thereby an overlapping of the laterally placed ones is avoided.' 



We see that in strongly illuminated twigs anisophylly almost dis- 

 appears, in feebly illuminated ones, on the other hand, it is strongly 

 marked, and I particularly direct attention to this because the dorsiven- 

 trality here has been considered by many authors as an effect of gravity. 

 Kny 1 , for example, takes this view on account of the following in- 

 vestigation : ' Many twigs of Abies pectinata were firmly fastened in an 

 inverted position at the beginning of November, 1871. As these unfolded 

 their buds in the spring of 1872 without undergoing lateral torsion the 

 horizontal position of the leaves underwent a change in correspondence 

 with their new direction so that the dorsal side was turned upwards and 

 the ventral side was turned downwards ; on the other hand the aniso- 

 phylly was retained in the same sense as it would have been in the normal 

 position, that is to say, the upper leaves were the longer, the under leaves 

 the shorter. The relationship of the longest to the shortest leaves was 

 only slightly modified. It was not until the spring of 1873, quite a year 

 and a half after the beginning of the experiment, that the influence of 

 the new direction was undoubtedly evident in the proportional develop- 

 ment of the leaves, and showed itself in this, that on the new shoots 

 which were laid down by the mother-shoot in succession corresponding 

 with its inverted position the anisophylly exhibited inversion in corre- 

 spondence therewith.' This experiment shows clearly that the anisophylly 

 is already determined in the bud. I have proved the same in the buds 

 of Aesculus Hippocastanum -, which develop anisophyllous shoots even 



1 Kny, Uber die Bedeutung der Florideen in morphologischer und histologischer Beziehung und 

 den Einfluss der Schwerkraft auf die Coniferenblatter, in Botan. Zeitung, 1873, p. 433. 



2 Goebel, Uber einige Falle von habitueller Anisophyllie, in Botan. Zeitung, iSSo, p. 840. 



