20 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



" derogatory " in the use of the terms. They only signify the dis- 

 appearance more or less completely of certain parts with the altera- 

 tion and development of others. The whole process is simply the 

 result of self-adaptation to new conditions of life. 



The new conditions may be of various kinds, such as an increase or 

 decrease of water, alterations in the nature of the soil, a deficiency of 

 Hght, as in woods, varying amounts of heat, as well as parasitism 

 and saprophytism. Each of these factors may so affect the organism, 

 when the seeds have germinated under new conditions, that unless 

 they can adapt themselves to the totality of effects they must perish. 

 Within limits all plants possess this power of responding adaptively 

 to changes in their environment. Then, if they continue to live for 

 several generations under the same conditions, the newly-acquired 

 characters tend to, and usually do, become relatively if not absolutely 

 fixed and hereditary. 



Hence arise species with a few or more degenerate organs about 

 them. Such degraded features are taken note of by systematic 

 botanists, as " specific characters." Thus, the name depauperata 

 is not infrequently given as specific or varietal, suggesting the fact 

 that starvation was the cause of the degenerate features. 



The two most important factors which cause degeneration are 

 excess and deficiency of water, as in aquatic plants and those of 

 heaths and deserts respectivety. 



Examples of Aquatic Degradation.— -Let us take as an example 

 of the former the aquatic buttercup known as the Water-Crowfoot, 

 We may safely assume that it has descended from some terrestrial 

 species. It is familiar to all by its numerous little white flowers 

 standing out of the water and its completely formed leaves floating 

 on the surface, while the submerged leaves are finely dissected like 

 fennel. Hence it has the name Ranunculus heterophyllus. Another 

 species is still more degenerate, for it has no floating leaves at all, and 

 is called the "hair-leaved," Ranunculus trichophylkis. If a floating 

 leaf of the former happen to have one half of it below the surface, 

 that half always becomes dissected. Moreover, numerous other 

 genera of various families, respectively, often have a species, or the 

 family may have a whole genus, aquatic, while all the rest are 

 terrestrial. When this is the case, all the aquatic ones, as a very 

 general rule, have similar dissected leaves. 



Hence we are justified in inferring that submergence, or rather the 

 water, is responsible for the dissected type of foliage. To prove 

 experimentally that the dissected t5^e of leaf is the actual result of 

 degradation through the effect of water, nutritive salts were dissolved 

 in it ; the consequence was that not only was the superfluous water 

 within the plant discharged (which had so saturated the proto- 

 plasm that it was too weak to make a complete leaf), but as soon as 

 it had absorbed the nourishment perfectly formed leaves were sub- 

 sequently developed under water. 



From this experiment we may generaUze upon the deteriorating 



