108 



from morphological differences, Mr. Sansom proceeded to 

 say : — It is necessary therefore that I should describe in as 

 few words as possible the sense in which I use the term 

 Species. By species, then, are meant such individuals as are 

 supposed to have been formed at the creation of the world, 

 and contmued by propagation or reproduction ever since. 

 Thus a species embraces those plants which, from a close re- 

 semblance to each other, are presumed to have proceeded from 

 one common origin, the seeds of which produce similar plants. 

 There may, however, be trifling differences in unimportant 

 points, such as colour, size, etc., which though sufficient to 

 constitute varieties, are not incompatible with a common 

 origin. Varieties usually owe their origin to soil, exposure, 

 excess of moisture, or other causes, and have a tendency to 

 return to their original type. 



Botanical characters may be taken from the existence or 

 non-existence of certain organs, or they may be taken from 

 their size or shape, or the degree in which those characters 

 exist ; but before any real or permanent use can be made of 

 any of these appearances, it is necessary to form an estimate 

 of their constancy; for however good this or that character 

 may appear to be in one tribe of plants, it may be equally 

 valueless in another ; or perhaps this anomaly may exist in 

 individuals of the same genus. Indeed I shall be able to show 

 that many, very many, of the most valuable botanical charac- 

 ters in ordinary use, are in some tribes so very uncertain that 

 we cannot place any reliance upon them. 



In the marsh plants, cases are not unfrequent where the 

 form of the leaf varies so considerably from excess of moisture, 

 or other causes; as to raise doubts in the minds of observers 

 unacquainted with the habit of those peculiar plants, whether 

 or not they may be distinct species ; and it is only by the pro- 

 duction of intermediate states that we can solve these diffi- 

 culties. Again, on the chalky downs of Kent and Surrey, we 

 often find plants possessing a downy epidermis, so variable in 



