.^,. DR. WEISMANN'S THEORY OF HEREDITY. 177 



be the direct cause, is the fact that the species of cultivated plants 

 often, if not generally, " sport " simultaneously in various districts, 

 and even in different countries. Thus, I am assured that double 

 Petunias were never raised until they simultaneously appeared in 

 one and the same season in France, Germany, and England. 

 Similarly, Chrysanthemums are known to furnish sports of a like 

 kind in different places. Now, although double flowers, as of 

 Petunias, are mostly propagated from cuttings, yet, speaking 

 generally, they can be perpetuated by seed and intensified by 

 self- fertilisation. It was thus that Mr. Veitch raised his " Balsami- 

 floral " section of East Indian Rhododendrons, and others raised 

 double Begonias. 



Again, there is a class of phenomena which are designated as 

 " habits," as of insectivorous, parasitic, saprophytic, and climbing 

 plants, &c. These are scattered over the vegetable kingdom, often 

 without any affinities, respectively ; and when one imagines the 

 Jirst individual of any species which acquired any one of these habits, 

 becoming, e.g., parasitic, such a habit must have been a character 

 acquired during the lifetime of the individual. Yet, in all cases 

 these habits, and the anatomical structures correlated to them, are 

 now hereditary. 



As other instances in which peculiar structures are now heredi- 

 tary may be mentioned aquatic plants, and those possessing 

 subterranean stems. Whether they be dicotyledons or mono- 

 cotyledons, there is a fundamental agreement in the anatomy of 

 the roots and stems of aquatic plants, and, indeed, in many cases, 

 in the leaves as well. Such has hitherto been attributed to the 

 aquatic habit. The inference or deduction was, of course, based 

 upon innumerable coincidences ; the water being supposed to be 

 the direct cause of the degenerate structures, which are hereditary 

 and characteristic of such plants in the wild state. 



M. Costantin has, however, verified this deduction by making 

 terrestrial and aerial stems to grow underground and in water. One 

 could not say, a priori, what alteration would take place, if any at all ; 

 but the new structures at once begin to assume the subterranean or 

 aquatic types, as the case may be ; and, conversely, aquatic plants 

 made to grow on land assume the terrestrial type of structure ; 

 analogous results following changes from a subterranean to an aerial 

 position, and vice versa. This verification, therefore, proves not only 

 that the influence of the environment is at once felt by the organ, 

 but that it was indubitably the cause of the now specific and heredi- 

 tary traits peculiar to normally aquatic, subterranean, and aerial 

 stems or roots. 



The difference in structure between the upper and under side of 



a horizontal leaf is known to be interchangeable, according to the 



incidence of light ; while erect leaves, equally exposed, are similarly 



constructed on both sides. Here, as in all organs, we discover by 



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