HEREDITY, AND THE ORIGIN OF SPECIES MACDOUGAL. 509 



and horticulturists have made early observations of direct interest in 

 this connection. Thus Dr. Arthur Hollick, while a student at Colum- 

 bia University in 1879, said in writing of white varieties of colored 

 plants : 



First, then, we have to consider those sports of nature where there has been 

 a sudden change, without any intermediate steps, from a plant with colored 

 flowers to a pure white variety ; such may be termed " negative " varieties, 

 since their peculiarity is due rather to an absence of color than to the presence 

 of white. Not only does the flower show the characteristic absence of color, 

 but the leaves, stem, and, in fact, the entire plant, are invariably of a lighter 

 green; and if any red be normal to the stem (which is often the case) this 

 will also be of a lighter shade. It has often been urged that these albinos are 

 mere " sports " of nature with nothing constant about them * * * and that 

 there is nothing inherent in the constitution of the plant. Fortunately, I have 

 been able to test this * * * and found them * * * not only constant 

 in their peculiarities, but also that these are bred in the plant and capable of 

 Inheritance. 



Three years later, about the time that De Vries began casting about 

 to find material suitable for the demonstration of his theory of unit- 

 characters and their saltatory action, Mr. Thomas Meehan, a horti- 

 culturist of Philadelphia, wrote as follows in a discussion of some 

 anomalous form of the oak : 



The conclusion that I have been forced to is that the odd forms we often 

 find in nature are not necessarily hybrids, but are as likely, if not more likely, 

 to be the outgrowth of some internal law of form with which we are as yet 

 unacquainted. That they do not often perpetuate themselves is [not, plainly 

 implied] remarkable when we remember that of thousands of seeds produced 

 on any one tree but a very small percentage ever gets a chance to form, and of 

 those which do sprout, again but a small percentage survives to become bearing 

 trees. As the number of trees reproducing the general features of the original 

 may be as a hundred to one of the more strikingly aberrant forms, we may see 

 that though individual instances may be common, we are never likely to meet 

 many trees of one stamp. Once in a while an individual tree may find itself 

 in a situation favorable to the preservation of a number of seedlings, which 

 might endure until again reproductive ; in such cases a marked variety may 

 originate and make its way over the earth. 



I have often thought it probable that in time a few individuals of these 

 suddenly introduced forms might again leap into new features, and then, if they 

 should be able to sustain themselves, we should have new species quite inde- 

 pendently of any principle of natural selection ; that principle, as I understand 

 it, being governed chiefly by " environment." 



These utterances may be taken as prophetic in part, and in part as 

 a natural expression of the inadequacy of explanations of the origin 

 of species current at the time. Shortly afterwards, Professor de 

 Vries, impressed with the necessity for obtaining positive evidence 

 upon the subject, began an examination of the plants in the vicinity 

 of Amsterdam, Holland. Over a hundred species were brought into 

 cultivation and tested by guarded pedigree cultures, and every pre- 



