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THE AMERICAN NATURALIST [Vol. XLV 



Generally speaking, the investigation of the flora of a 

 newly discovered or formerly inaccessible region is a 

 matter of choice or, better, perhaps, opportunity. The 

 same is true for the detailed study of our collective 

 species, leading to a recognition of component elements 

 as illustrated by the work of Small on Oxalis, 10 Rhus, etc. 

 Whoever can devote a part of his time to the study of a 

 genus is able to establish the existence of differences 

 which, formerly ignored and in themselves slight, are of 

 the greatest importance for the tracing of relationships. 

 Unfortunately, perhaps, in such studies there is usually 

 developed a mass of detail so great, so intricate that none 

 but a few specialists are able to recognize the various 

 forms. Hieracium, Aster, Cyperus are names sufficient 

 to strike terror in the hearts of any but the most ardent 

 systematists. But before such a detailed study can be made 

 there must be gathered, in the first place, herbarium mate- 

 rial. It is not sufficient to possess a single specimen. 

 Material must be collected from various habitats and 

 both during the flowering and fruiting periods. Often 

 there are differences between the leaves of old and 

 young shoots, as in Crataegus. Or the leaves of the 

 fruiting branches may be different from those of purely 

 vegetative shoots as in Hedera Helix. Ficus and PotJws 

 both may show leaves of a very different character. 11 

 None would at first sight believe leaves of seedlings or of 

 adventitious shoots of Eucalyptus globulus and those of 

 older specimens to belong to the same species. Many 

 species of Acacia show, during the first few years of 

 their existence, well-developed phyllodes which later dis- 

 appear entirely. Sometimes even the leaves on the same 



""North American Flora," 25': 25, 1907. 



11 In the greenhouses of the Missouri Botanical Garden may be seen a 

 very fine specimen of Ficus repens which near the ground and up to a 

 height of some eight feet, produces the small leaves typical of this species. 



large leaves are produced. Other instances are given in de Vries's "Species 

 and Varieties," Ch. 15. 



