January 25, 1895.] 



SCIENCE. 



97 



catastrophe wliieli acoompanies the sudden 

 onrusli of summer. •• One by one the 

 flowei-s fade and go to seed, if they have 

 been fortunate enough to attract a bee or 

 other suitable poUen-bearing visitor. The 

 arri\al of summer hapjjens so late that the 

 inexperienced traveler may be excused for 

 sometimes doubting whether it really is 

 coming at all. When continuous night has 

 become continuous day without any percep- 

 tible approach to spring, an Alpine traveler 

 naturally asks whether he has not reached 

 the limit of perpetual snow. During May 

 there were a few signs of the possibility of 

 some mitigation of the rigors of winter. l)ut 

 these were followed by frost. At last, when 

 the final victory of summer looked hoj^less, 

 a change took place : the wind turned to 

 the south, the sun retired behind the clouds, 

 mists obscured the landscape, and the snow 

 melted ' like butter upon hot toa.st,' and we 

 were in the midst of a blazing hot summer 

 picking flowers of a hundred different kinds 

 and feasting upon wild ducks' eggs of vari- 

 ous species." 



The polypetalous families which blossom 

 early in the season, although old geologi- 

 cally speaking, have not been gi'eatly modi- 

 fied since Pliocene times, because their 

 flowers open in the spring before the Lepi- 

 doptera hatch out from their cocoons. It 

 is obvious that every species of flower can 

 only be visited and fertilized by those in- 

 sects which occur at the time when the 

 plant is in flower and in stations where it 

 grows. The insect visitors of a plant are 

 therefore limited by the season and by the 

 time of day when it flowers, by its geogra- 

 phical distribution and by the nature of its 

 habitat. The high northern polypetahe 

 have remained therefore regular while 

 those plants gi'owing in the southland have 

 become highly irregular by the visits of 

 numerous liighly organized insects in great 

 number near the equatorial zone. We 

 must be cautious, however, in generalizing 



too broadly, for we can only call those parts 

 perfect which fulfill their purpose in the 

 life of the plant essentially well; that is to 

 say, which under existing conditions insure 

 the sexual reproduction of the species with 

 particular success. 



The Composit;e (sun-flower family), the 

 highest expression of evolution amongst 

 Dicotyledons, appeared latest in geological 

 succession, for no undoubted form of them 

 (Sj-nanthene ) has been found farther back 

 than the middle Pliocene. Muller says:* 

 '• The numerical preponderance which this 

 family has attained in species and genera 

 (1000 ) , and the extreme abundance of many 

 of the species, are due to the concurrence of 

 several characters, most of which singlj-, or 

 in some degree combined, we have become 

 acquainted with iu other families, but never 

 in such happy combination as in the 

 Compositie. The following points deserve 

 special mention: (1) the close association 

 of many flowers; (2) the accessibility of the 

 honey as well as the plentiful secretion and 

 security from rain; (3) the possession of a 

 pollen mechanism, which renders cross fer- 

 tilization certain iu the event of insect visi- 

 toi-s." It is a ma.sterful order of plants 

 most commonly met with in the late sum- 

 mer aud autumn, flowering profusely until 

 the heavy frosts of early winter, when they 

 cast their seeds abundantly. An enumera- 

 tion of the Compositie growing in the vicin- 

 age of Philadelphia shows that the plants 

 are essentially late summer growers. 



'^ MiiUer, The Firlilizntion of Flowers. 



