DORSIVENTRAL SHOOTS. ANISOPHYLLY IN HEPATIC AE 101 



spicuous. A glance at the representation of Cyathophorum pennatum 

 in Fig. 54 will suffice for the recognition of this, and according to the 

 statements in the literature l the larger leaves are inserted upon the 

 side which is turned to the light and the smaller ones are upon the 

 under side, as is the case in liverworts. The larger leaves of Cyathophorum, 

 and more so those of some species of Hypopterygium, for example 

 Hypopterygium fuscolimbatum, are asymmetric like those of many dorsi- 

 ventral shoots of the higher plants ; they are divided by the leaf-nerve 

 into two unequally large parts of which the smaller is overlapped, and 

 this again seems to indicate that the smaller leaves lie upon the shaded 

 side. As I have only been able to examine dried material I am unable 

 to say with certainty whether this is always so. 



B. HEPATICAE. 



Anisophylly and its relation to dorsiventrality and to plagiotropous 

 growth appears in a very striking manner in the foliose (' acrogynous ') 

 Jungermannieae. In them the stem clings to the substratum, although 

 I have satisfied myself that they are positively heliotropic in very feeble 

 light ; seldomer they are obliquely ascending, as in Mastigobryum. 



The shoots have three rows of leaves, two of which are lateral and 

 the third is on the under side composed of much smaller, very often 

 extremely reduced, leaves which are called amphigastria. These leaves 

 are derived from the segments of a three-sided pyramidal apical cell 

 which turns one of its sides to the substratum. In those forms which possess 

 fully developed amphigastria the apical cell has an equal-sided triangular 

 projection, whilst in those which have either reduced amphigastria or 

 none at all the side of the apical cell turned to earth is smaller than the 

 others. The dorsiventrality is then already expressed in the structure 

 of the vegetative point. The lateral leaves are originally inserted trans- 

 versely to the long axis of the shoot, but they are subsequently displaced 

 so that their upper surface is turned upwards, and their insertion becomes 

 either oblique or comes to be almost in the long axis of the shoot. 

 This however occurs, so far as my experience goes, only in the forms 

 in which the leaves are developed as flat plates; where the leaves have 

 the form of cell-rows the displacement does not take place, for example, 

 in Jungermannia trichophylla and Arachniopsis. Such displacement 

 brings .the leaves into a favourable light-position, and, according to my 

 investigations, light is the direct cause of it in many cases. As a conse- 

 quence of it the lateral leaves have frequently an asymmetric con- 

 struction, the ' lower lobe ' being smaller than the ' upper lobe,' whilst 



1 C. A. Miiller, Synopsis mnscorum frondosorum, vol. ii. p. 3. 



