54 



NATURE 



{R'lay 20, 1 8 So 



frequent in the family. So constantly does the labellum 

 appear to act as a resting-place for insects, that in 

 trying to trace the probable manner in which they fer- 

 tilise a species, you naturally loolc upon it as the plat- 

 form of the operator ; but in this case, should a tiny 

 insect alight upon one of the lips which hang trembling 

 from the flowers, it would meet with a projection re- 

 sembling the column and in the same position usually 

 occupied by it, but without anther or stigma, being in fact 

 nothing more than the hinge from which the fringed lip 

 depends. This baffling is caused by the flowers being 

 inverted, and the dropping of the labellum in front of 

 them. Such modifications as this are useful in checking 

 the natural tendency to assume that a certain part of a 

 flower is designed to act in a certain way simply because 

 through a long scries we find it performing that function, 

 and to show us how a slight change may alter all the 

 results. Here the labellum bars access from the ordinary 

 direction ; the lower sepal incloses the column from 

 below ; the petals and wings of the column intercept 

 access from the sides, and a prolongation of the anther 

 obstructs it from the end ; so that a very small space is 

 left open beneath the labellum in what would appear to 

 be the least likely place for an insect to approach, though 

 from the conformation of the column the intervention of 

 insects seems to be a necessity. After a very careful 

 examination, I came to the conclusion that the most 

 probable method in which this interesting little orchid 

 becomes impregnated is by a very minute insect alighting 

 on the under surface of the labellum and following it up 

 into the flower, the lip giving way to its pressure upwards 

 (by being lifted on the hinge) should the visitor be slightly 

 too large. Would not the chances of the reproduction of 

 this species be improved by the removal of the labellum ? 

 This, then, is another instance of a part of a flower, 

 generally of importance, becoming of very doubtful 

 advantage, if not actually detrimental." 



Hitherto Mr. Fitzgerald's studies have been confined to 

 the orchids of Eastern Australia, but it is most earnestly 

 to be desired that they will be extended to the southern 

 and western species, as indeed the title of his work 

 implies will be the case. 



LETTERS TO THE EDITOR 



\Tlie Editor does not hold himselj responsible Jor opinions expressed 

 by his correspond, nts. N'either can he undertake to return, or 

 to correspond with the writers of, rejected manuscripts. A'o 

 notice is taken of anonymous communications. 



[The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otheiiuise to .ensure the appearance even of com- 

 munications containing interesting and novel facts.\ 



Ice-Crystals 



Since the publication of the Duke of Argyll's first communi- 

 cation on "Ice-Crystals" (Natuke, vol. x.\i. p. 274), I have 

 been expecting that some of the physicists who have noticed 

 similar phenomena would have looked up the literature of the 

 subject. 



About thirty years ago I made this class of phenomena the 

 subject of a somewhat careful investigation, and published the 

 results of my researches in the Proc. Am. Assoc, for Adv. of Sci., 

 third meeting, March, 1850, vol. iii. pp. 20-34; also in the 

 Phil. Mag., 3rd series, vol. xxxvi. pp. 329-342, May, 1850. 

 'Y\it former article is illustrated by several engravings represent- 

 ing the appearances presented by the "exudation of ice " from 

 the foot-stalks of the Pluchca. I tliink that my investiga- 

 tions show tliat the plienoraenon in plants \i purely physical, 

 having no connection with the vitality of the stems ; and that it 

 is due to the same cause as the "protrusion of icy columns" 

 from the ground in frosty weather. 



In relation to the explanation of the phenomena, I have 

 nothing to add to that given in the above-mentioned paper, 

 except in relation to two points, viz. (i), that I did not sufficiently 



emphasise the importance of the fact that the water contained in 

 the capillary tubes in the upper stratum of earth is cooled 

 many degrees below the freezing temperature ; and (2) that, 

 consequently, the congelation wouldj necessarily talce place 

 paroxysmally. '' John Le Conte 



Berkeley, California, April 27 



Anchor-Ice 



Mv remarks on anchor-ice, pubU^hed iu Nature, vol. xxi. 

 p. 53S, have called forth several letters to myself, in addition to 

 the articles on this subject by Mr. Allan Macdougall and C. F. C. 

 respectively, which have a place in vol. xxi. p. 612 and vol. xxii. 

 p. 31 of your journal. I am happy to find that C. F. C. agrees 

 generally with my views, but I regret to have to differ from him 

 when he says that " the original (ice) crystals, if not heavier than 

 v'ater, are at least as heavy." Were this supposition true, 

 anclior-ice might as readily form in one part of a stream as in 

 another, and would not require the conditions which I beheve 

 to be necessary. These minute crystals have never been seen by 

 me "distributed" pretty evenly thioughout the body of water at 

 rest, nor even where there was a smooth, slow, steady current, 

 which would be the case if the specific gravi'y of the crystal and 

 water were alike. 



C. F. C. is right in saying that this ice resembles manufactured 

 "water ices"; it is never, as far as I know, transparent. It 

 also looks like salt-water-ice. 



Mr. Macdougall tells us of anchor-ice in Georgian Bay. This 

 at first sight would appear to be incompatible or at variance 

 with my belief in the necessity of a "comparatively swifter 

 current " being e,-fential for this formation, but to those who are 

 familiar with the large lakes of America, the apparent contra 

 diction seems not difficult of explanation. 



At Great Bear Lake inexplicable currents of several miles an 

 hour, sometimes running against the wind, are found in many 

 of the narrow and shallow channels separating islands from the 

 shore, making agitation sufficient to disturb the equi'.ibrium of 

 the floating ice-crystals and surface cold water. The same 

 condirion of things doubtless obtains in the Georgian Bay, which 

 is .the most easterly portion of the extensive and irregularly- 

 shaped Lake Huron. 



One remark of Mr. Macdougall's, to the effect that "the 

 anchor-ice in the great northern lakes floats at a considerable 

 depth under the surface of the water, and that it seemed to be 

 floating at various depths in water fourteen feet deep," is curious. 

 One way of accounting for this peculiarity may be that when the 

 air becomes detached from the bottom, it not improbably brings 

 up with it stones or gravel ; soon afterwards a part of the ice 

 gets separated, thus diminishing the floating-power, until the 

 specific gravity of the compound mass exactly equals that of 

 water, in vihich condition it might, of course, be found 

 "swimming" at any depth below the surface. 



Mr. Macdougall asks, "Does the (anchor) ice form by action 

 of the intense cold of the ground (meaning, I presume, the 

 bottom of the lake or stream), favouring the formation of 

 rasee?" 



1 do not think that as a rule the coldness of the ground has 

 anything to do with this formation, except in so far as this cold- 

 ness of the ground, i.e., the stony bottom, is caused by contact 

 with the ice-cold water and ice-crystals, as already mentioned. 

 " Intense coldness " of the ground at the bottom of the middle 

 of a stream can scarcely be caused by abstraction of caloric, 

 through its connection with the supposed colder land on shore, 

 which is usually covered and protected by snow from cold in 

 early winter ; also, were this the cause, or one of the causes, the 

 part of the river nearest the shore would first show anchor-ice, 

 which is not the case. 



At Repulse Bay flooding'of some of the rapids of North Pole 

 River took place when the ice was forming. This \\e know 

 could not he. caused by a greater Aovi of water, as the lakes 

 supplying the river and all the rivulets running into them were 

 already firmly ice-bound. 



These overflows were caused by barriers of anchor-ice, which 

 dammed the water up to the height of two or three feet, untU the 

 pressure became so great as to force a passage through the soft 

 but tenacious mass, the portion of which that remained unbroken 

 being now, by the running oft' of the water, brought into contact 

 with the cold air, soon became frozen hard and solid. 



J. Rae 



4, Addison Gardens, W., May 15 



