284 YIEWS, &C. PHYSIOGNOMY OF PLANTS. 



relations are the result of my investigations for seven great 

 families of the vegetable kingdom in one and the same tem- 

 perate zone : 



Glumaceae 1 (Grasses alone JL.) 



Composite -L 



Leguminosae ^ 



Labiatse Jj 



Umbelliferse J_ 



Amentaceae (Cupuliferse, Betulinese, and Salicinese) JL. 



Cruciferse -J^ 



The forms of organic beings are reciprocally dependent on 

 one another. Such is the unity of nature, that these forms 

 limit each other in obedience to laws which are probably con- 

 nected with long periods of time. When we have ascertained 

 the number of the species on any particular part of the 

 earth's surface belonging to one of the great families of 

 the Glurnaceae, the Leguminosoe, or the Composite, we may 

 with some degree of probability, form approximative con- 

 clusions regarding the number of all the phanerogamia, 

 as well as of the species belonging to the other families of 

 plants growing in the country. The number of the Cy- 

 peroidea3 determines that of the Composita3, and the number 

 of the latter determines that of the LeguminosaB ; and these 

 estimates, moreover, enable us to ascertain in what classes and 

 orders the Floras of a country are still incomplete, teaching 

 us w T hat harvests may still be reaped in the respective families, 

 if we guard against confounding together very different 

 systems of vegetation. 



The comparison of the numerical proportions of families in 

 the different zones which have as yet been well explored, has 

 led me to a knowledge of the laws which determine the nu- 

 merical increase or decrease of vegetable forms constituting 

 a natural family, in proceeding from the equator to the poles, 

 when compared, for instance, with the whole mass of phane- 

 rogamia peculiar to each zone. We must here have regard 

 not only to the direction, but also to the rapidity or measure 

 of the increase. We see the denominator of the fraction, 

 which expresses the ratio, increase or diminish. Thus, for 

 instance, the beautiful family of the Leguminosae diminishes 



