II. PERMANENCE OF SPECIES. 59 



reasouing from facts to causes and consequences. The 

 Author of the Cybele Britannica still retains the views 

 set forth in the Phytologist for 1845; and the concluding 

 summaiy of those views may here be appropriately 

 quoted ; with a reference to the periodical mentioned for 

 the arguments and facts in more detail. 



" The conclusion, that ' like produces like,' through an 

 indefinite series of generations, seems almost inevitable 

 to the botanist, whose range of observation takes in only 

 the natural course of events during the quarter of a 

 centur}', more or less, which comprehends the period of 

 vigorous mental power in a single individual. The same 

 conclusion must still appear sound, although we extend 

 the range of observation, by comparing living plants of 

 the present year, with careful descriptions, pictorial repre- 

 sentations, or dried specimens of those which lived a 

 hundred years ago. Still the same conclusion must be 

 drawn, when we compare a young oak or chestnut with 

 old trees of their kind which have existed through centu- 

 ries past, 



" Thus far, the resemblance between the past and the 

 present, in the vegetable world, is sufficiently close and 

 certain to warrant a conclusion that plants repeat their 

 own images by hereditary descent through a long series of 

 years, to which we can assign no limit. 



" These images, it is true, are not always perfect like- 

 nesses. Variations of climate and soil, or of other con- 

 ditions, are accompanied by corresponding variations in 

 the plants. But, limiting the period of our observations 

 as above, these variations are usually found to be tempo- 

 rary ; so that we may say, there is a standard or average 

 type for each kind, which is repeated in the individual 

 plants as nearly as internal health and external conditions 

 will allow. This supposed standard or average I will 



