110 THE INDUCTIONS OF BIOLOGY. 



we still find the limit of growth to have a great 

 range. The smallest branched flowering plant is extremely 

 insignificant by the side of a forest tree ; and there is an 

 enormous difference in bulk between the least and the great- 

 est mammal. But on comparing members of the same 



species, we discover the limit of growth to be much less vari- 

 able. Among the Protozoa and Protophyta, each kind has a 

 tolerably constant adult size ; and among the most complex 

 organisms, the differences between those of the same kind 

 that have reached maturity, are usually not very great. 

 The compound plants do, indeed, sometimes present marked 

 contrasts between stunted and well-grown individuals ; but 

 the higher animals diverge but inconsiderably from the 

 average standards of their species. 



On surveying the facts with a view of empirically general- 

 izing the causes of these differences, we are soon made aware 

 that by variously combining and conflicting with each other, 

 these causes produce great irregularities of result. It be- 

 comes manifest that no one of them can be traced to its 

 consequences, unqualified by the rest. Hence the several 

 statements contained in the following paragraphs, must be 

 taken as subject to mutual modification. 



Let us consider first, the connexion between degree of 

 growth and complexity of structure. This connexion being 

 involved with many others, becomes apparent only on so 

 averaging the comparisons, as to eliminate differences among 

 the rest. Nor does it hold at all where the conditions are 

 radically dissimilar ; as between plants and animals. But 

 bearing in mind these qualifications, we shall see that 

 organization has a determining influence on increase of 

 mass. Of plants the lowest, classed as Thallogens, 



usually attain no considerable size. Lichens, Algae, and Fun- 

 gi, count among their numbers but few bulky species : the 

 largest, such as certain Algae found in antartic seas, not 

 serving greatly to raise the average. Though ^among 

 Acrogens there are some, as the Tree-ferns, which attain a 



