24 



NA TURE 



{May 14, 1874 



Bernoulli's numbers, and on points connected with definite 

 integrals. — Prof. Wolstenholme's papers are concerned 

 with series and loci, and treat also of epicycloids and hypo- 

 cloids. — Mr. T. CotteriU gives a short paper on an alge- 

 braical form and the geometry of its dual connection with 

 a polygon, plane or spherical. — An analogous theorem 

 relating to polyhedra is discussed by Prof. Clifford in this 

 same volume. — M. Hermite contributes two short notes, 

 one on circular functions, the other on unicursal curves. — 

 Mr. J. J. Walker writes on the invariant conditions of 

 multiple-concurrence of two conies, and Mr. R. B. Hay- 

 ward on an extension of the term Area to any closed 

 circuit in space. — From this analysis it will be seen that 

 there is considerable variety in the contents of the volume. 

 It is not necessary here to give any detailed account of 

 the papers, as notices of them have appeared from time 

 to time in our columns. 



LETTERS TO THE EDITOR 



Tlie Editor does not hold himself responsible for of inions expressed 

 by his eorrespondents. No notice is taken of anonymous 

 communications .] 

 Flowers of the Primrose destroyed by Birds 

 I HOPE that you will permit me to make a few final remarks 

 on the destruction of primrose flowers by birds. Eat first I 

 must return my best thanks to your correspondents, as well as 

 to some gentlemen who have written direct to me, and to whom 

 I have not had time to send separate answers. Secondly, I 

 must plead guilty to the high crime of inaccuracy. As the 

 stalks from which the flowers had been cut were shrivelled, I 

 mistook, in a manner now inexplicable to me, the base of the 

 ruptured or removed ovarium for the summit ; a remnant of the 

 shrivelled placenta being mistaken for the base of the pistil. I 

 have now looked more carefully, and find that on twelve stalks 

 only three had any remnant of the ovarium left. I have also 

 examined sixteen bits of the calyx which had been cut off by a 

 caged bullfinch, presently to be noticed, and in fifteen of these 

 not only had the ovarium been torn into fragments or quite 

 destroyed, but all the ovules had been devoured, excepting some- 

 times one or two. In several cases the calyx had been split 

 open longitudinally. The ovarium was in the same state in 

 thirteen small portions of the calyx lying on the ground near a 

 wild cowslip plant. It is therefore clear that the ovules are the 

 chief attraction ; but the birds in removing by pressure the 

 ovules could not fail to squeeze out the nectar at the open 

 end, as occurred when I squeezed snnilar bits between my 

 fingers. The birds thus get a dainty morsel, namely, young 

 ovules with sweet sauce. I still think that the nectar is, in 

 part, the attraction, as caged bullfinches and canary birds 

 much like sugar ; but more especially because Mr. C. J. Monro 

 has sent me some flosvers from a cherry-tree near Barnet, which 

 during several years has been attacked ; and he finds many of 

 the flowers, both those on the tree and on the ground, with 

 rather large ragged holes in the calyx, like, but much larger 

 than, those often made by humble bees when they rob flowers in 

 an illegitimate manner. Now the inside of the flower of the 

 cherry, round the ovarium, is bedewed (if protected from the 

 visits of insects) with drops of nectar, which sometimes collect 

 so as almost to fill up the bottom of the flower. In the case of 

 the cherry I cannot doubt that this is the attraction, for I ex- 

 amined the ovarium of ten flowers, and although they had all 

 been scored by the bird's beak, and in four instances punctured, 

 the ovule had in no case been devoured. 



To return to the primroses : from the accounts received, it 

 seems that the flowers are cut off in the manner described by 

 me, near Preston in Lancashire, in North Hampshire, Devon- 

 shire, and Ireland, as well as in Kent. In several other places, not 

 worth specifying, where primroses are abundant, they have not 



been thus attacked ; and this may possibly be due to the proper 

 enemy, namely, as I now suspect, the bullfinch, not being a 

 common bird. In my former letter I remarked that if the 

 habit of cutting off the flowers proved to be a widely ex- 

 tended one, we should have to consider it as inherited or 

 instinctive ; as it is not likely that each bird should discover 

 during its individual lifetime the exact spot where the nectar, 

 and, as I must now add, the ovules, lie concealed, or should 

 learn to bite off the flower so skilfully at the proper point. 

 That the habit is instinctive, Prof. Franklaud has given me in- 

 teresting evidence. When he read my letter he happened to 

 have in the room a bunch of cowslip flowers and a ca^ed bull- 

 finch, to whom he immediately gave some of the flowers, and 

 afterwards many primrose flov/ers. The latter were cut off in 

 exactly the same manner, and quite as neatly, as by the wild birds 

 near here. I know that this is the case by having examined the 

 cut-off portions. The bird worked so quickly that he easily de- 

 stroyed twenty flowers in three minutes ; a single wild pair 

 would therefore cause great havoc. Prof. Frankland informs me 

 that his bird pressed the cut-off portions of the calyx in its beak, 

 and gradually worked them out on one side, and then dropped 

 them. Thus the ovules were removed, and the nectar neces- 

 sarily squeezed out. A canary bird to whom some cowslip and 

 primrose flowers were given attacked all parts indiscriminately, 

 and ate up the corolla, calyx, and stalks. A lady also informs 

 me that her canary and siskin always attack primrose and cow- 

 slip flowers, if kept in the same room. They generally first 

 make a ragged hole through the calyx opposite the ovarium, and 

 remove the ovules, as I found to be the case with flowers which 

 were sent to me ; but the ovules had not been so well removed 

 as by the bullfinch, and the nectar could not be obtained by this 

 method of attack. 



But now comes the interesting point : the caged bullfinch just 

 referred to was caught in 1872 near Ventnor, in the Isle of 

 Wight, soon after it had left the nest, by which time the prim- 

 roses would have been out oi flower, and since then, as I hear 

 from Prof. Frankland, it had never seen a primrose or cowslip 

 flower. Nevertheless, as soon as this bird, now nearly two 

 years old, saw these flowers, some machinery in its brain was 

 set into action, which instantly told it in an unerring man- 

 ner how and where to bite off and press the flowers, so as 

 to gain tlie hidden prize. We are reminded by this little fact of 

 Mr. Spalding's admirable observations on the instinctive actions 

 of chickens when their eyes were uncovered, after having been 

 blind-folded from the moment of being hatched. 



Prof. Frankland seems to have been much struck with the 

 behaviour of his bullfinch, and remarks in his letter that "it 

 had all the precision of a chemical reaction ; the result of putting 

 a primrose within its reach can be almost as certainly predicted 

 as that of putting a plate^of iron into a solution of sulphate of 

 copper." Cn.\RLEs D.\r\vin 



Down, Beckenham, Kent, Iilay 7 



P.S. — This letter was printed before I saw your last number, 

 and I am glad to find that some of my statements are confirmed, 

 more especially with respect to bullfinches. During the last fort- 

 night not one primrose has been attacked in the little wood 

 where shortly before there was such havoc. I imagined that the 

 pair of bullfinches, which I saw there earlier in the season, had 

 wandered away ; but yesterday evening (May 10) it occurred to 

 me that the flowers produced late in the season might fail to 

 secrete nectar, or that the recent cold weather might have pro- 

 duced this effect. Accordingly, in the afternoon I gathered 

 fifteen flowers from as many distinct plants, and kept them in 

 water in my room for seventeen hours. Earlier in the season I 

 treated some flowers in this same manner, and found the tube 

 of the corolla full of nectar ; but now only one of the flowers 

 contained a very small ^quantity] of uectar, another showing a 



