No. 539] 



ORIGIN OF SPECIES IN NATURE 



645 



shoot may present a very different appearance. And 

 while this is something not entirely unexpected in hy- 

 brids as in Quercus Leana (Q. coccineaXimbricaria) and 

 Boston fern hybrids, it is a source of astonishment when 

 this occurs in species which we do not believe to be of 

 hybrid origin. Heterophylly is a matter of common 

 observation in the ubiquitous horseradish, Radicula 

 Armoracia. Sterculia diversifolia, commonly cultivated 

 in greenhouses, has leaves which are mostly ovate t<> 

 lanceolate in outline and which are often entire or vari- 

 ously three- to five-lobed on the same shoot. The sassa- 

 fras, S. variifolium, illustrates the same principle, in 

 fact, derives its name from this feature. The paper mul- 

 berry, Broussmietia papj/rifera, shares the irregular 

 lobing of the leaf with its near relatives, Morus rubra 

 and M. alba} 2 The cut-leaved Persian lilac is very 

 variable in this respect. 13 Sometimes seasonal differ- 

 ences are so great as to make collecting throughout the 

 year an absolute necessity, 14 an instance so strikingly 

 illustrated by Viola palmata. In woody plants there is 

 not infrequently a return to the nepionic stage in the 

 leaves produced near the base. 15 When we remember 

 that heterochromatism 16 may add a further complication, 

 it becomes evident that it is not sufficient to be able to 

 refer to herbarium specimens only. The living plant 

 must be studied in its various stages of development. It 

 is by this means only that one may arrive at a true esti- 



mate of the stability and significance of n 



2: 569. 



