6oo 



NA TURE 



{April 30, 1885 



"Land-locked salmon" is admitted to be a race of the true 

 Salmo salai, which from some cause having lost its migratory 

 instinct, now lives in lakes, never migrating seawards, while its 

 size is less than that of its sea-going relative. But as the two 

 species are really the same, a cross between a land-locked salmi in 

 and a trout in fish-cultivation would be identical with a cross 

 between a Salmo solar and a trout. 



What then has been the result of attempting the latter cross at 

 Howietown during the last few years? November 25, 1879, this 

 was effected between salmon milt and Lochleven trout eggs ; up to 

 now all the offspring have been sterile, none have attempted to 

 spring out of the ponds, and the largest fish among them last 

 year, although in good condition, was only 16^ inches long. On 

 December 24, 1881, this cross was again made, with similar 

 results, the largest fish last winter being about 12 inches long. 

 (Examples are in the South Kensington Museum). Sterility, I 

 may remark, was anticipated from this cross, while it was sup- 

 posed that such would remove the anadromous instinct, and 

 these results have occurred, but as regards improvement in size, 

 such has not, so far, proved a success. 



A cross was made between a young salmon par and a Loch- 

 leven trout, on November 29, 1S83, but the young succumbed to 

 blue dropsy of the sac. This cross was again tried November 14, 

 1884, when the par was a year older, and so far the young look 

 well, but we can scarcely anticipate their proving fertile off- 

 spring. I say "scarcely," for we know that domestication 

 eliminates sterility in some races of hybrids, and in this instance 

 the par had been raised from eggs at Howietown ; these have 

 now grown into grilse without descending to the sea, and given 

 eggs. Eggs thus furnished from Howietown-raised grilse have 

 hatched, and several thousand young par are in the establish- 

 ment, the future of which race will be an interesting study. 



I think I am justified in advising that when crossing salmon 

 with trout, not to select a parent from a river or lake, but, if 

 possible, to obtain eggs or milt from a race of salmon which has 

 been two or more generations in a semi-domesticated condition, 

 as with such the probabilities of failure are considerably lessened, 

 but, so far as I have witnessed, hybrids between salmon and 

 trout have proved sterile and undersized. 



Cheltenham Francis Day 



Forms of Leaves 

 In a recent issue of Nature, in the discussion on the forms 

 of leaves, Mr. Henslow seems to doubt the assertion of Sir John 

 Lubbock that the holly produces prickly leaves on the lower- 

 branches, and smooth leaves without spines above ; but this is a 

 fact which may easily be verified in numerous localities (selected 

 gardens varieties are of course not intended). I know of a large 

 tree at Kew which altogether confirms the statement. The ex- 

 planation, however, that the spines of the lower leaves may be 

 produced to prevent animals from browsing on them, and that 

 they are not developed on the upper branches because these are 

 beyond the reach of animals, seems to me to require some modi- 

 fication, if not to be given up altogether, in this limited sense. 

 It seems to me to admit of a much simpler explanation, namely, 

 that it is an approximation — or reversion, if indeed the term be 

 applicable — to the ancestral type. It is a well-known fact that 

 in the embryonic stage of an organism the affinity with the 

 ancestral type is best seen, and that in the mature stage the 

 greatest amount of specialisation takes place ; and, viewed in 

 this light, the case of the holly does not appear to present much 

 difficulty. A young seedling is seen to have very spiny leaves, 

 but with increasing age the leaves becoming comparatively spine- 

 less. In the case of the furze we have the most overwhelming 

 evidence that the spiny character has been developed to repel 

 the attacks of herbivorous animals, and a young seedling is seen 

 to have trifoliate leaves — like the laburnam — from which we 

 infer that its ancestral type was spineless, and had trifoliate 

 leaves. The large group of nhyllodineous Acacias bear an 

 equally unmistakable stamp of their origin in the bipinnate 

 leaves which the seedlings at first produce. In most cases these 

 leaves are very early superseded by phyllodes, but in A. melano- 

 xylon the habit of producing true leaves is never quite lost. 

 There is a large tree of this species about 40 feet high at Kew, 

 at the south end of the Temperate House, close to the spiral 

 staircase. It is thus in an admirable position for examination. 

 At the base of this tree the leaves predominate over the phyllodes, 

 but in ascending the staircase the proportion is seen to gradually 

 diminish, till at the top of the tree — a few feet above the gallery 

 — scarcely a true leaf is to be seen. Assuming the mature stage 



to be the more highly specialised, we have in the holly a pre- 

 cisely parallel case. This necessarily involves the opinion that 

 the ancestral type of the genus Ilex had spiny leaves ; and, if so, 

 it seems highly probable that the character was developed as a 

 protection against the attacks of herbivorous animals. A poss- 

 ible objection which at first struck me was that many of the 

 species have quite smooth leaves ; but this has been removed by 

 a search through the specimens in the Kew Herbarium. In the 

 first place, species with spiny leaves occur in each great centre 

 of distribution of the genus — in North and South America, India, 

 China and Japan, the Atlantic Islands, as well as Europe — and 

 in the second, although no seedling plants were found, there are 

 three species which show very spiny leaves on barren branches, 

 and smooth leaves on the more mature flowering branches. 

 These are /. insignis and /. dipyrena, from India, and /. Perado, 

 from the Atlantic Islands. I have little doubt that seedlings of 

 many species would present the spiny character if we could only 

 see them. The presence of spines — the nerves being extended 

 beyond the margin of the leaf — seems to indicate an excess of 

 vascular over cellular tissue ; a condition which is either modified 

 with increasing maturity or is not exhibited in the same pheno- 

 mena. In any case a severe pruning — or reduction of the parts 

 to be nourished — is followed by a temporary reversion to the 

 more spiny character. If this explanation be the correct one the 

 question naturally arises, Why are the hollies losing the property 

 of producing spiny leaves? rather than, Why does the holly 

 produce spiny leaves on its lower branches ? The answer to the 

 first query would perhaps be, Because they no longer need the 

 protection afforded by the spines. To the second, Long-con- 

 tinued habits are not often instantly laid aside. 



Herbarium, Kew, April 18 R. A. Rolfe 



Kite-Wire Suspended Anemometer Readings 

 Having lately made some observations with my anemometers 

 elevated, as above described, at heights above the ground con- 

 siderably greater than those mentioned in my paper before the 

 British Association last year, I venture to think that a word or 

 two as to the main point at present under investigation, viz. the 

 general increase in the velocity with the altitude at heights 

 between 600 and 1100 feet above the ground, may be interesting 

 to your reader^. 



Up to June last the greatest altitude reached by the anemo- 

 meters was 646 feet. I have lately been able to secure readings 

 up to 1 129 feet. Taking the average of seven of these, we get 

 the following values for the mean relative velocities at two mean 

 heights : — 



Height in feet Velocities in 



above ground. feet per minute. 



1070 2297 



756 2l6 s 



When these values are inserted in the formula - -= ( - j ,weget 



for the value of the exponent x — o'i7, or a little more than £ ; 

 but when 500 feet — the elevation of the place of observation 

 above the sea — are added to each elevation, we get x = C26, or 

 almost exactly \, which is the value I deduced for the exponent 

 in Nature (vol. xxv. p. 506), from a discussion of Dr. Vettin's 

 cloud observations. 



I would not at present lay much i-stress upon this coin- 

 cidence until I have investigated the ratio up to heights of 

 2000 feet or more, but I certainly think it supports the notion 

 that the formula with this exponent represents the average law 

 of increase at heights over 1000 feet above sea-level. 



E. Douglas Archibald 



Temperature of the Body of Monotremata 

 I have found the temperature of the body of Echidna hyslrix 

 to be (average of three observations) 28 0, o C, and that of 

 Ornithorhynchus paradoxus (two observations) 24°'8 C. 1 



These temperatures present a special interest, comparing them 

 with the mean temperature of the body of mammalia in general, 

 which is (after Dr. J. Davy's observations of thirty-one different 

 species) 38"'4 C. N. de Miklouho-Maclay 



Biological Station, Watson's Bay, near Sydney, 

 N.S.W., March 10 



' Details of these observations can be found in the Proceedings of the 

 Linnean Society of New South Wales, vol. ix. pp. 425 and 1204. 



