ORIGINAL COMMUNICATIONS. 



On the Study of Plant Associations. 



By Eobert Smith, B.Sc. 



It has long been recognised that a close connection exists between 

 the kind of vegetation of a country and the prevailing conditions of 

 climate and soil, and that changes in the one, either in space or in 

 time (phenology), bring about corresponding changes in the other. 

 Thus many works on the flora of a region have been supplemented by 

 a general account of the conspicuous vegetation in the landscape, the 

 chief trees, the nature of the stations, etc., correlating this with the 

 general climatic conditions of the region. This general account, at 

 first vague and unmethodical, has gradually become more and more 

 organised into a definite survey of the " Vegetation," as contrasted with 

 the " Flora." For long it remained hardly more than a branch of 

 descriptive geography, employed as indicative of the climate and 

 economic wealth of a country, but within recent years the subject has 

 assumed an important biological position, and now may be taken to 

 represent a description of the relations which exist between the plant- 

 coverino; of a region and the conditions of life. 



The floristic method of study, on the one hand, is more directly 

 concerned with the historical development of the " flora." It attempts 

 to answer the questions, How have these species originated ? or whence 

 have they come ? It studies phylogeny and migration ; and the 

 botanical characters to which it directs attention are those on which 

 we chiefly rely for indications of racial affinity, namely, those of the 

 floral organs. 



In considering the "vegetation," on the other hand, the essential 

 characters of the species are those indicating adaptation to the environ- 

 ment, and are to be found mainly in the vegetative organs. Hence 

 groups of similar adaptational form, " Lebensform " of German authors, 

 need by no means coincide with natural families or groups of species. 

 For example, Empetrum and Erica, or Aloe and Agave, possess similar 

 " life-forms," and could be grouped as Ericoid-forms and Aloe-forms 



8 NAT. SC. VOL. XIV. NO. 84. IO9 



