172 The Phenomena of Morphogenesis 



dorsiventral and anisophyllous and much resemble those of Lycopodium 

 (all tending to grow horizontally). 



There are other plants in which the occurrence of anisophylly seems 

 much less directly dependent upon environmental factors and occurs 

 throughout the plant. This "habitual" anisophylly, as Goebel calls it, is 

 probably to be interpreted as a genetic tendency to develop in this way 



vu 



Fig. 7-10. Diagram of a horizontally grown branch of maple, showing anisophylly. 

 The vertically oriented pair of leaves (VU, VL) differ greatly in size but are sym- 

 metrical. In the horizontally oriented pair (HL, HR), the lower half of each leaf is 

 larger than the upper. ( From Sinnott. ) 



under such a wide range of environments that it has become essentially 

 an inherited trait. In many foliose liverworts, for example, the axis has 

 three rows of leaves, two of them lateral and the third, the much 

 reduced amphigastria, borne on the under side. Most species of Sela- 

 ginella have four rows of leaves: two lateral and relatively large and the 

 other two on the upper surface between these and somewhat smaller. 



