162 



SCIENCE 



[N. S. Vol. XXXIII. No. 840 



serious mistakes. Thus plants and trees 

 often flower at an abnormal time after 

 receiving serious injury.* This is really 

 one form of tendency to eliminate the dis- 

 turbing factor. One should also distin- 

 guish between the direct injury to the 

 plant or animal and the change in the 

 organism which enables it or its descend- 

 ants to withstand the disturbing influences. 

 A great deal has been done in the way of 

 collecting facts illustrating the effect of 

 environment on plants and animals: but 

 the real reason for any particular change 

 is rarely given," and the change is only too 

 often the resultant of two or more factors 

 which are not differentiated carefully. I 

 am going to cite some eases in which the 

 application of the theorem of Le Chatelier 

 is quite clear, and also others which seem 

 interesting enough to warrant attention 

 being called to them. 



PRESSURE AND CONCENTRATION 



The wind blows against the trees and the 

 boughs bend so as to spill the wind. A 

 prevailing wind from a given direction 

 causes the trees to assume a permanent set. 

 This is not especially interesting because 

 this change is probably not inherited to 

 any appreciable extent. 



Bailey^" has pointed out that plants tend 

 to become circular instead of bilateral, be- 

 cause they are sessile. 



They therefore found it to their advantage to 

 reach out in every direction from their support 

 in the search for food. Whilst the centrifugal ar- 

 rangement has strongly tended to disappear in 

 the animal creation, it has tended with equal 

 strength to persist and to augment itself in the 



' Mobius, " Lehre von der Fortpflanzung der 

 Gewiiehse," 6, 122, 1897. 



» Cf. Bailey, " The Survival of the Unlike," 32, 

 1896; MacDougal, Memoirs N. T. Bot. Garden, 2, 

 1, 1903; Crozier, "The Modification of Plants by 

 Climate," 1885; Eimer, "Organic Evolution," 

 1890. 



""The Survival of the Unlike," 15, 1896. . 



plant creation. Its marked development amongst 

 plants began with the acquirement of terrestrial 

 life, and with the consequent evolution of the 

 asexual or sporophytic type of vegetation. Nor- 

 mally, the higher type of plant bears its parts 

 more or less equally upon all sides, and the limit 

 to growth is still determined by the immediate 

 environment of the given individual or of its 

 recent ancestors. Its evolution has been aceph- 

 alic, diffuse or headless, and the individual plant 

 or tree has no proper concentration of parts. For 

 the most part it is filled with unspecialized 

 plasma, which, when removed from the parent 

 individual (as in cuttings or grafts), is able to 

 reproduce another like individual. The arrange- 

 ments of leaves, branches, the parts of the flower, 

 and even of the seeds in the fruit, are thus rotate 

 or circular, and in the highest type of plants the 

 annual increments of growth are disposed in like 

 fashion; and it is significant to observe that in 

 the compositae, which is considered to be the 

 latest and highest type of plant-form, the rotate 

 or centrifugal arrangement is most emphatically 

 developed. The circular arrangement of parts is 

 the typical one for higher plants, and any de- 

 parture from this form is a specialization, and 

 demands explanation. 



In England rabbits are held in check, 

 though with some difficulty. If the repres- 

 sive factors are removed, as in Australia, 

 the rabbits adapt themselves to the situa- 

 tion and multiply so as to become a veri- 

 table pest. In the same way the Russian 

 thistle spread through the northwest some 

 years ago. An insect will often adapt 

 itself to changed conditions to such an 

 extent as to take on new habits.^^ 



An early naturalist traveling in Colorado 

 found a striped beetle feeding upon wild solanums 

 or nightshades. The insect came to be in demand 

 among collectors, and it is said that handsome 

 prices were paid for specimens for museums. In 

 the course of time the settlers grew potatoes in 

 Colorado and the insect took a fancy to them and 

 spread rapidly. It is now known as the Colorado 

 potato-beetle. The first attacks were noticed about 

 thirty years ago, but now the insect is a serious 

 pest wherever potatoes are grown in quantity. 



"Cf. Bailey, "The Survival of the Unlike," 

 184, 1896. 



