442 



SCIENCE. 



[Vol. VII., No. 171 



flowers in which one or more of the sepals had 

 been transformed into petals, as shown in fig. B ; 

 and, from their evident relation to each other, the 

 author notices the fact as deserving the attention 

 of those who would speculate upon laws of varia- 

 tion and heredity. 



From the description it will be seen that the 

 flowers are conspicuous, having deep-yellow pol- 

 len, dark blood-red stamens and pistil, snow- 

 white petals, and dark sepals, all unhidden by the 

 foliage. But, notwithstanding this conspicuous- 

 ness, the flowers are seldom visited by bees, there 

 being, as was found, little or no nectar or honey 

 to attract them. Even in cases where bees were 

 observed upon the flowers, the prominent pistil 

 did not readily admit of fertilization. The author 

 was surprised, however, to find that soon after 

 blossoming very many of the petals were severed 

 near the middle, or at the base, by a single strong 

 incision. By watching he soon discovered the 

 cause to be birds of the genus Thamnophilus. 

 These birds, of which the male is black and the 

 female brown, alighted usually upon a branch 

 above the one on which a flower was in bloom, 

 and, reaching downward, bit off the petals ; but, 

 in so doing, either the neck or forehead invariably 

 came in contact with the anthers, and brushed off 

 the pollen, leaving the flower as seen in fig. C. 

 Whether birds of this genus, especially in the 

 more normal habitat of the tree in the higher 

 lands of Brazil, are the only agency of cross- 

 fertilization, or whether other birds share in it, re- 

 mains to be discovered. 



In Europe it is only exceptionally that birds are 

 attracted by flowers. Sparrows sometimes bite 

 off the flowers of the yellow crocus, and the bull- 

 finch will pluck with inherited dexterity that por- 

 tion of the under part of the primrose which con- 

 tains honey. No adaptation has hitherto ever 

 been observed where such mutilations of the blos- 

 som were of direct advantage to the plant, and 

 the present example of Feijoa is therefore the 

 more remarkable for the high degree of perfec- 

 tion which this adaptation has reached. Instead 

 of the sweet petals being spread out for ornament 

 alone, out of which the bird could pluck but a 

 small portion, they become rolled up, thus per- 

 mitting a larger part to be bitten off, and present- 

 ing greater attractions. The stout, firm anthers, 

 and pistil, are likewise adaptive, insuring the 

 clinging of the pollen to the feathers of the bird, 

 and thus its ready transportation from one blossom 

 to another. 



How these adaptations have been brought about 

 can scarcely be conjectured, as the genus is widely 

 removed from the allied genera, and there are no 

 intermediate forms. 



PROFESSOR HUGHES ON SELF-INDUCTION. 



The recent researches of Prof. D. E. Hughes, 

 president of the Society of telegraph engineers 

 and electricians, have been extended by him, and 

 his latest results will be published in a forthcom- 

 ing number of the Society's journal. We are en- 

 abled to give some account of these researches 

 from an account published in Engineering. 



The extra resistance of a wire during the ' vari- 

 able period,' that is to say, when the electric cur- 

 rent entering it is rising to its normal strength, 

 has been shown by Professor Hughes to proceed 

 from an extra current of opposite name self -in- 

 duced in the wire. He finds, however, that there 

 are cases in which this effect is reversed, so as to 

 produce less resistance in the wire during the 

 variable period. Such cases occur when ex- 

 tremely fine wires are being tested with powerful 

 currents ; for the steady current heats the wire, 

 thus introducing an extra resistance. The induc- 

 tion-bridge of Professor Hughes enables him to 

 study and analyze these effects, tracing them to 

 their true cause. 



Professor Hughes has lately been investigating 

 the self-induction of coils, as well as of straight 

 wires, and the following table gives his result : — 



Coils formed of 3 metres of silk-covered copper 

 wire 1 millimetre in diameter, each coil being ~ 

 millimetres in diameter. 



One coil alone 



Two similar coils in series 



Two similar coils in parallel, but separated 5 centi- 

 metres from each other 



Same two coils in parallel, but superposed 



One single coil of thicker wire of exactly the same 

 form, length, and resistance as the two coils in 

 parallel - 



£35 



u O 



eS © e3 w 

 O 



100 

 174 



55 

 81 



75 



This table shows an increase of the self-induc- 

 tion when the two coils are in series, but not 

 quite double the effect, as there is an increased or 

 added resistance. This result is well known ; but 

 a more interesting result is obtained where the 

 two coils are parallel and separate, giving 32 per 

 cent less self-induction than when they are super- 

 posed, and 26 per cent less than that of a single 

 coil of the same resistance. Professor Hughes 

 traces this result to the reaction of contiguous 

 coils on each other. 



With regard to the self-inductive capacity of 

 non-magnetic wires of different metals, but of 

 the same lengths and diameters, Professor Hughes 

 finds that when non-inductive resistances, say, of 

 carbon, are added to the wires to bring them to 

 equal resistance, there is apparently no difference 

 in the self-inductive capacity of all the metals he 

 has yet tried ; but if, instead of adding a supple- 



