330 UETEROMOEPHY. 



dimensions as another; one flower resembles very closely 

 another flower of the same age and so on. Nevertheless 

 it occasionally happens that there is a very considerable 

 difference in form in the same organs, not only at 

 different times, but it may also be at the same time. 

 Descriptive botanists recognise this occurrence in the 

 case of leaves, and apply the epithet heterophyllous to 

 plants possessed of these variable foliar characters. 

 In the case of the flower, where similar diversity of 

 form occasionally exists, the term dimorphism is used. 

 As these phenomena appear constantly in particular 

 plants, they are hardly to be looked on, under such 

 circumstances, as abnormal, but where they occur in 

 plants not usually polymorphic, they may be considered 

 as coming within the scope of teratology. 



Heterophylly. As a general rule, the leaves or leaf- 

 organs in each portion of a plant, from the rhizome or 

 underground axis, where it exists, to the carpellary 

 leaf, have their own special configuration, subject only 

 to slight variations, dependent upon age, conditions of 

 growth, &c. The cotyledons are very uniform in 

 shape in each plant, and are scarcely ever subject to 

 variation. The leaves near the base of the stem, the 

 root-leaves as they are not unfrequently called, some- 

 times differ in form from the stem-leaves ; these again 

 differ from the bracts or leaves in proximity to the 

 flower. The floral envelopes themselves, as well as 

 the bud-scales, all have their own allotted form 

 in particular plants, a form by which they may, in 

 most cases, be readily recognised. Hence, then, in 

 the majority of plants there is naturally very consider- 

 able difference in the form of the leaf-organs, accord- 

 ing to the place they occupy and the functions they 

 have to fulfil ; but, in addition to this, it not unfre- 

 quently happens that the leaf-organs in the same por- 

 tion of the stem are subject to great variation in form. 

 This is the condition to which the term heterophylly 

 properly applies. The variation in form is usually 



