July 19, 1907] 



SCIENCE 



71 



collected on the island of Sachalin by F. 

 Schmidt, but his speciaiens lack flowers. 



P. A. Etdberg 



New Yokk Botanical Garden 



.SCIENTIFIC BOOKS 



An Investigation of Evolution in C'hrysomelid 

 Beetles of the Genus Leptinotarsa. By 

 William Lawrence Ti>wer. Washington, 

 D. C, Carnegie Institution. 

 It has been an obvious criticism of many 

 of the recent experimental and statistical in- 

 vestigations of matters connected with evolu- 

 tion that they were entirely too narrow in 

 their scope. Even the famous studies of the 

 evening primroses, by de Vries, suffered from 

 the fact that their author did not really know 

 as much about the species of QHnothera as was 

 desirable, and was even ignorant of the orig- 

 inal habitat of the species giving rise to so 

 many remarkable mutations. The de Vriesian 

 studies attracted so much attention that it was 

 not long before many skilled botanists were 

 hot on the trail of the missing data, and to-day 

 the whole subject is on a very much better 

 footing. 



Professor Tower, in his work on the Colo- 

 rado potato beetle and its allies, has not de- 

 pended upon results obtained in the laboratory 

 alone, but has undertaken a comprehensive 

 study of the whole of the genus Leptinotarsa, 

 and even of the related genera, in the field. 

 He has compiled all the information extant 

 in the literature of the subject, and has made 

 repeated trips to Mexico and elsewhere to col- 

 lect and study the beetles in their native 

 habitats. He has found Mexico to contain a 

 large number of species of Leptinotarsa, hav- 

 ing characteristic habitats and habits, all of 

 which he has described, with photographic 

 illustrations. vSouthern Mexico, it is con- 

 cluded, is the center of origin of Leptinotarsa, 

 and consequently the Mecca of whoever would 

 seek to unravel the secrets of its evolution. 



It IS not possible, of course, to give a sum- 

 mary of these ecological investigations in a 

 review, but as an example we may quote from 

 some of the remarks on Leptinotarsa unde- 

 cimlineata : 



An instructive illustration of the manner in 

 which the dispersion of this beetle takes place was 

 afforded by the recent building of a railroad 

 through a perfectly flat, frequently flooded savan- 

 na near Tierra Blanca. The food plant grows 

 generally over the savanna, but the beetle is en- 

 tirely absent excepting at a few points along the 

 road where tlie work of constructing ditches to 

 keep the roadbed intact has created new localities 

 with favorable conditions for their existence. Over 

 a distance of about 18 kilometers there are now 

 located flourishing colonies at each place where 

 the work of the railroad builders has made exist- 

 ence possible, while on the unmodified savanna 

 I have not been able to locate a single colony, and 

 doubt if there are any. In this instance the ad- 

 vance into a new area has occupied two years and 

 has been rapid. That transportation [by human 

 means] did not bring about the starting of these 

 colonies is certain, as the work of railroad con- 

 struction was entirely suspended during the rainy 

 season, when the beetles are active and dispersion 

 takes place. It is perfectly clear that in this case 

 the distribution was brought about by some few 

 individuals from a colony happening by chance to 

 discover the newly created habitat, proper for 

 sestivation and for the breeding of the next genera- 

 tion. In each generation many will perish by not 

 being able to reach the proper habitat after once 

 having abandoned the parent colony, but the fact 

 remains that some do discover proper habitats, 

 and when such are found new colonies are estab- 

 lished. ... It is not necessary that th? soil should 

 be of a special chemical composition or tempera- 

 ture and rainfall of special amounts, but it is 

 essential that during pupation and aestivation the 

 beetle shall not be subjected to excessive desicca- 

 tion or moisture, and that the soil shall be porous 

 enough to admit of an abundant supply of air. 



This, indeed, is real biology; and how dif- 

 ferent from some ecological writings we have 

 seen! 



When we come to the potato beetle, L. de- 

 cemlineata, the discussion is most comprehen- 

 sive. The most interesting fact brought out 

 is the retreat of L. juncta, of the southern 

 states and Atlantic seaboard, before the in- 

 vading hordes of decemlineata. Now these 

 two species have different food plants, and so 

 apparently should not compete! It appears, 

 however, that they freely cross, and 



