IOO 



RELATIONSHIPS OF SYMMETRY 



compound leaves acquires a foot-stalk and leaflets that are large in proportion to 

 the supply of light ; and hence, as we descend towards the bottom of the tree, the 

 clusters of leaves display increasing contrasts.' 



Subsequently Hofmeister 1 , Wiesner 2 , and 

 Frank 3 gave attention to anisophylly. The term 

 has come to us from Wiesner, although his 

 definition, which is as follows, is too narrow 4 : 

 ' I mean by anisophylly that the leaves lying upon 

 the upper side of prone shoots have smaller 

 dimensions than those upon the under side, whilst 

 the lateral ones are intermediate.' We know, 

 however, that the leaves on the under side may be 

 smaller, as is the case in the foliose Jungerman- 

 nieae and in Lycopodium complanatum :> . I was 

 the first to show in some very striking examples 

 that in habitually anisophyllous shoots we have to 

 deal with photo-plagiotropy 6 . 



The following examples of anisophylly 

 are selected from different groups : 



A. Musci. 



Most of the shoots of the Musci are 

 orthotropous and isophyllous ; some of the 

 plagiotropous shoots are isophyllous, for ex- 

 ample, in the plagiotropous species of Hyp- 

 num. The plagiotropous foliage-shoots of 

 Mnium undulatum 7 (Figs. 28 and 29) usually 

 exhibit an indication of anisophylly inasmuch 

 as the leaves which stand upon the upper 

 side are somewhat smaller than the others, 

 but this is only slightly marked. The 

 anisophylly in Cyathophorum, Racopilum, 

 and Hypopterygium is much more con- 



1 Hofmeister, Allgemeine Morphologic derPflanzen, 1868. 



- Wiesner, Beobachtungen iiber den Einfluss der Erd- 

 schweie, in Sitzungsber. d. Wiener Akad. d. Wissensch., 

 Iviii (1868). 



3 Frank, Uber die Einwirkung der Gravitation auf das 

 Wachstum einiger Pflanzenteile, in Botan. Zeitting, 1868. 



4 Wiesner, Untersuchungen iiber den Einfluss der Lage 

 auf die Gestalt der Pflanzenorgane, I.e. ci (1892), p. 694. 



5 The cause of anisophylly will be discussed in the Fifth 

 Section. 



6 Goebel, Uber einige Falle von habitueller Anisophyllie, 

 in Botan. Zeitung, 1880, p. 839. 



1 The sexual shoots are orthotropous. 



FIG. 54. Cyathophorum 



pennatum. Tristichously- 

 leaved dorsiventral shoot 

 with the leaves upon the 

 side uppermost in the 

 figure smaller than the 

 others ; upon this side also 

 the short fertile branches 

 with small shortly-stalked 

 sporogonia stand. Some 

 leaves are wanting in the 

 lower part of the shoot. 

 The shoot arises from a 

 creeping, probably sympo- 

 dial, rhizome which bears 

 roots (rhizoids). The 

 larger leaves are asymme- 

 tric, the smaller ones are 

 not so. 



