422 



SCIENCE. 



[Vol. I., No. 1.5. 



while, at the point of growth in the root, only leuco- 

 plastides are to be seen. Moreover, in following the 

 plastides farther back, he found thera present in the 

 seed itself; and this he conjoins with the well-known 

 fact, that chlorophyll-granules are to be found ready 

 formed in certain seeds. 



The destiny of the plastide depends upon the tissue 

 which is to be developed from the meristem. Some 

 of them remain colorless, that is, as leucoplastides, 

 and serve to produce starch-grains at the expense of 

 assimilated matters; others become chloroplastides 

 to produce assimilated matter; while still others are 

 to furuish colors to flowers and fruits. This simplest 

 of all organs is therefore capable of wide metamorpho- 

 sis, by which it becomes fitted for its diverse functions. 



Kor is this all. The same plastide can become at 

 different stages of its lite a leuco-, a chloro-, and a 

 chromo-plastide. But which of these is the primal 

 form '? To this the author answers unequivocally, 

 the chloroplastide; and he believes that the others 

 have all been derived therefrom. Reserving some 

 of the other features of this suggestive paper for 

 another notice, it may be said that the terms pro- 

 posed by Schimper are quite equivalent to those 

 given by Van Tieghem in his Botany, now in course 

 of publication, as leucites and chloroleucites, and, in 

 part, to his xaiitho-leucites ; but, so far as their de- 

 velopment is concerned, the latter author follows the 

 accepted view of Gris. G. L. Goodalb. 



LETTERS TO THE EDITOR. 

 MoUuscan rock-boring. 



^ Ix giving lectures upon building-stones my atten- 

 tion has been often called to the action npon them of 

 boi'ing mollusks, echini, annelids, sponges, etc., when 

 used in submarine constructions. 



In Albany Hancock's paper on the above subject 

 {Ann. mag. nat. hist, (2), ii. 22.5, pi. viii.), are figured 

 numerous siliceous grains, found about the foot and 

 . mantel, which he regarded as secreted by the moUusk, 

 and employed in excavating the burrow. While Han- 

 cock's conclusions are generally denied, I have not 

 seen any explanation of the observed particles. The 

 forms figured by him, especially in fig. 6, resemble 

 the grains (principally quartz) observed in the micro- 

 scopic study of mud and other earthy deposits. Such 

 grains would naturally be the result and not the cause 

 of the rock e.xcavation ; and it is difficult to see how 

 the animal could be in the position in which it is 

 found, without their presence about it. 

 _ Perhaps some zoologist can state if this explana- 

 tion has been given before, and whether it be correct 

 or not. M. E. Wadswobtii. 



Cambridge, Mass., April 30, 1883. 



The Lake Superior rooks. 



Prof. N. PI. Winchell is evidently right in saying, 

 in Science, Xo. 12, that, in my letter in No. 5, 1 mis- 

 represented his position on the unconformity in the 

 St. Croix valley. I had said that he had strenuously 

 denied this tmconformity, because my recollection of 

 a conversation on the subject, held with him in 1880, 

 was to that effect. But, on turning to the reference 

 he gives in his First annual report of the geological 

 survey of Minnesota, I see that he had announced 

 such an unconformity as long ago as 1872, which, of 

 course, I should have known before; so that I must 

 have misunderstood him. 



As to the other matter, — viz., the relation of the 

 'St. Croix' or Potsdam sandstone of the Mississippi 

 valley to the ' eastern sandstone ' of Lake Superior, — 

 I certainly have understood from his various reports. 



that he regarded them as distinct. But I am very 

 glad to be set right on these points, though regretting 

 very much having misunderstood Professor Winchell; 

 for it narrows down the question at issue between us 

 very materially. R. D. Irving. 



Track of meteor. 

 In your first number, Feb. 9, 1883, I saw an ac- 

 count of a meteor witnessed by Capt. Belknap of the 

 U. S. S. Alaska, Dec. 15, 1882, and reference to a 

 similar phenomenon seen at Lake Winnipeg Jime 29, 

 18li0. On the evening 

 of June 17, 1873, in 

 early twilight, and be- 

 fore any stars were 

 visible, upon coming 

 out of my hotel in Vi- 

 enna, I found a crowd 

 of persons watching a 

 similar phenomenon, 

 which appeared to be 

 just north of the Kah- 

 lenberg. Upon in- 

 quiry, I learned that 

 a meteor had been 

 seen to fall a few mo- 

 ments before, but 

 without noise; and a 

 subsequent watch of 

 the daily papers gave 

 no account of any 

 meteorite, which 

 could hardly have es- 

 caped observation in 

 this settled section of 

 Austria. It would ap- 

 pear, therefore, that 

 this meteor must have been entirely dissipated in 

 vapor before reaching the earth. 



When I first saw the luminous track, I at once sup- 

 posed it, from appearance and color, to be the flame 

 from a distant zinc-furnace; but it was gradually 

 changed from its straight course to a curved line 

 closely resembling fig. 3 in Science, No. 1, p. 5, and 

 appeared to be borne to and fro by the gentle cur- 

 rents of air. It extended fully 30° from the horizon, 

 and was distinctly visible for half an hour after my 

 attention was first called to it. From a letter sent by 

 me the next day to a friend in this country, the above 

 facts are taken, in which letter I roughly sketched 

 the appearance of the luminous cloud, after a few 

 minutes from the fall of the meteor, as shown by the 

 accompanying cut. Peter Collier. 



AUGUSTUS DE MORGAN. 



Memoir of Augustus de Morgan ; loith selections 

 from his letters. By his wife, Sophia Eliza- 

 beth DE Morgan. London, Longm,ans, Green., 

 &f Co., 1882. 10, 422 p., portr. &°. 

 If the degree of interest which attaches to 

 the life of a hard-working mathematician is, 

 from the nature of the case, less than strong ; 

 if the biography of De Morgan is in this re- 

 spect in marlvcd contrast to that of a man 

 whose life is a picture of his time, and who has 

 had himself a distinct effect upon his time, — 

 to the life, sa^', of Harriet Martineau, which 

 was included within nearly the same years as 

 the life before us, — it is none the less true 



