52 



SCIENCE. 



[Vol. IV., No. 76. 



rotation commenced. The direction of the stems 

 can he well seen in figs. 6 and 2. 



The cause of this mode of growth being, of course, 

 the outward radial tendency of the plantlet in reac- 

 tion upon the centripetal force acting through the 



Figs. 2-7. 



soil, we may put the intensity of the new modifier 



equal to the centripetal acceleration, (rp) r. This 



gives a centrifugal ' force,' so called, of 5,348 degrees, 

 or 5.4 g, at a radius of six inches. If we put M O 

 (fig. 7) equal to gravity, and M N equal to this cen- 

 trifugal ' force,' then, for an ideal case, M P will 

 represent the resultant direction of the growing 

 rootlet. This is but very loosely approximate to the 

 observed positions, as might be expected. 



Chas. S. Slichter. 

 North-western university, Evanston, 111., 

 June 27. 



Perforations in -wool fibre. 



In my investigations in wool fibre I have found some 

 defective hairs that were perforated in places, evi- 

 dently while growing on the sheep's back. As the 

 perforations are perfectly circular, it would indicate 

 that they are made by some creature at present un- 

 known. Would it not be worth the while of some of 

 your scientific readers to examine into the matter, 

 and discover, if possible, what the perforator may be, 

 and whether it is likely to remain as little injurious 

 as at present ? Jos. M. Wade. 



Boston, July 7. 



The evolution of petals. 



In Mr. Grant Allen's interesting treatise on the 

 1 colors of flowers,' the first chapter deals with the evo- 

 lution of petals from stamens, in which the author 

 shows that petals are but specialized stamens set apart 

 for the purpose of attracting insects. His proofs are 

 such that no candid reader is likely to finish the chap- 

 ter, and apply its principles to the flowers he meets in 

 his every-day walks, without being convinced of the 

 correctness of the author's views. The gradual devel- 



opement from stamen to petal can be seen in most of 

 those cultivated flowers which exhibit a tendency to 

 become double, as well as in those which have already 

 become so. 



But it would seem that Mr. Allen had overlooked 

 one point in the method of evolution. Throughout 

 the entire book the idea is given that the process of 

 evolution begins by the filaments becoming flattened. 

 Thus, on p. 11, taking the English water-lily (Nym- 

 phea alba) as a typical example, the author says, — 



" In the centre of the flower we find stamens of the 

 ordinary sort, with rounded stalks or filaments, and 

 long, yellow anthers full of pollen at the end of each; 

 then, as we move outward, we find the filaments grow- 

 ing natter and broader, and the pollen-sacs less and 

 less perfect ; next we find a few stamens which look 

 exactly like petals, only that they have two abortive 

 anthers stuck awkwardly to their summits ; and finally 

 we find true petals, broad and flat, and without any 

 trace of the anthers at all. Here, in this very ancient 

 though largely modified flower, we have stereotyped 

 for us, as it were, the mode in which stamens were 

 first developed into petals, under stress of insect selec- 

 tion." 



Again, on p. 115, he says, "It has been objected 

 by two or three authoritative critics, that the original 

 petals need not have been yellow, because they rep- 

 resent the flattened filaments, not the anthers;" and 

 the author goes on to show that filaments are usually 

 of the same color as the petals. 



FLOWER OF CYDONIA VULGARIS, SHOWING TRANSFOF.MATION 

 OF STAMENS TO PETALS. 



An examination of a number of our common flow- 

 ers shows, that, in many cases at least, the evolution 

 of the petal begins with the anther rather than the 

 filament. Thus, in the common quince (Cydonia vul- 

 garis), many of the flowers possess stamens of which 

 the anthers have become petal oid, while the filaments 

 are of the normal type. Some of the anthers are 

 merely flattened on one end; others are more so; 

 while in others the anther has become a flat, white, 

 petaloid disk on the end of a normal filament. From 

 this, every gradation can be seen to the normal petal. 

 In this instance, not only the pollen-walls, but the 

 pollen itself, has become petaloid before the filament 

 has been at all modified. In the flowers of the mock- 

 orange (Philadelphus coronarius) the same transition 

 often occurs, as well as in many of the double flowers 

 of our gardens and conservatories. 



Clarence M. Weed. 



Agricultural college, Lansing, Mich. 



Metallic circuits in cables. 



When the full text of Mr. Gisborne's paper, read 

 before the Koyal society of Canada, is published, it 

 will be shown that his anti-induction experiments 

 with all metallic circuits in underground cables were 

 made in connection with an electric target, for which 

 a prize medal was awarded to him at the London 

 exposition of 1862; and the diagrams attached to his 

 paper will also explain why parallel metallic circuits 

 in a multiple cable, unless twisted according to his 

 design, will not eliminate induction of currents in 



