52 



SCIENCE. 



[Vol. XXII. No. 547 



during the night. This increase must have been due to absorp- 

 tion of water by the leaves. 



At 8.40 A.M. the bell- jar was removed to a window space and 

 the damp atmosphere was obtained within the jar as before. The 

 leaves of the plant were then thoroushly sprayed again and the 

 plant was placed under the jar and left there in a strong light 

 during the day. From time to time, as the water began to dis- 

 appear from the leaves, they were resprayed. At 4 p.m. the 

 plant was removed from the moist chamber and carefully dried. 

 It was then weighed and showed a loss in weight since 8.40 a m. 

 of 0.41 grams. 



On repeating the experiment with the same plant, the increase 

 in weight was 0.04 grams during the night— from 6.15 P.M. to 

 8.20 A.M. From 8.30 a.m. until 3.30 p.m., there was a decrease in 

 weight (transpiration) of 0.33 grams. 



But was the increase in weight during the night in these ex- 

 periments really due to absorption of water by the leaves? May 

 not the moist air surrounding the plant have passed through the 

 rubber covering and deposited some of its moisture upon the 

 earth or pot, thus giving absorption by the earth rather than by 

 the leaves? Such an interpretation of the experiment is forbid- 

 den by the condition of the interior found upon opening the 

 rubber covering at the close of the confirmatory experiment. 

 (That condition was not precisely known while the experiments 

 described were in progress, for the plant had been subjected to 

 experiments for several weeks, during which time its growth had 

 made it difficult to give to the plant amounts of water exactly 

 equal to the amounts transpired from day to day). Upon open- 

 ing the rubber covering, the earth in the pot was found wet to 

 the touch, the pot was wet, and the whole inner surface of the 

 rubber covering was wet. In this condition of things, the 

 greater movement of the water must have been from within the 

 pot outward through the rubber to its dry outer surface and the 

 drier — comparatively drier — air surrounding it in the moist cham- 

 ber. If such a movement of water did occur, its effect was that 

 of diminishing the weight of the plant during the night. We 

 must regard absorption by the leaves as the cause of the in- 

 crease which really occurred. 



How potent a factor light is upon the functions of the plant, is 

 readily seen by a comparison of the changes in weight dur- 

 ing the day in these experiments with the changes during the 

 night. At night, in the darkness, absorption perceptible by the 

 balance occurred ; during the day, transpiration predominated 

 although the leaves of the plant were kept wet with water and 

 in a moist atmosphere. Is it not possible that some of the 

 failures to find absorption by leaves may have come through nice 

 quantitative experiments having been carried on in the daytime, 

 as would be the more convenient ? 



In conclusion, the experiments so far as they have been carried, 

 seem to show — 



(a) That leaves may absorb water. 



(5) That leaves of growing plants do absorb water during the 

 night when they are wet with water and in a moist atmosphere 

 — i.e., under dew conditions. 



INDIVIDUAL SKELETAL VARIATION. 



BY FREDERIC A. LCOAS, U. S. NATIONAL MUSEUM, WASHINOTON, D. 0. 



The subject of individual skeletal variation is one of consider- 

 able interest, to the morphologist from the hints it may give con- 

 cerning lines of descent, to the systematic zoologist from its 

 bearing on the specific units of classification and to the vertebrate 

 paleontologist since he must mainly rely upon more or less frag- 

 mentary skeletons for the determination of species. 



External variationsare readily perceived, often easily accounted 

 for by known conditions of environment, but the question how 

 much may the skeleton of a given species normally vary is by no 

 means easy to answer. 



Unfortunately the problem is rendered all the more difficult 

 from the fact that the large series of specimens necessary for its 

 solution are seldom available, so that characters may be con- 

 sidered of specific value, or, on the other hand, as mere abnor- 



malities, when they are really normal variations or, perhaps, due 

 to changes brought about by age. The following notes are some- 

 vrhat desultory in their character, but they are based on the 

 observation of considerable series of individuals of the various 

 species referred to, and are brought forward as suggesting the 

 existence of a large amount of individual skeletal variation. 



In the report of the U. S. National Museum for 1887-88, the 

 writer gave at some length the results of the examination of a 

 large series of bones of the Great Auk, a series that was particu- 

 larly interesting from the fact that it represented adult individu- 

 als from one locality and one epoch, so that any variations might 

 be considered normal, and not due to differences of environment, 

 or to modifications that might gradually come about in the course 

 of time, even were there no change in surrounding conditioils. 



It may be briefly said that the long bones were found to vary 

 to the extent of one-fifth of their length, but that the most inter- 

 esting variations in the skeleton were the tendency to develop a 

 ninth, extra pair of ribs and the frequent presence of a small 

 tubercle on the tarsus, just where a hind toe would be located. 



Very nearly one sacrum out of every seven possessed facets, 

 showing the former presence of an abnormal number of ribs, 

 while but one twelfth of the tarsi showed the little tubercle re- 

 ferred to. 



Professor Newton found almost equally great variability in the 

 bones of the Dodo and Solitaire, birds of unusually restricted 

 habitat, but this he ascribes very largely to the fact that the 

 remains examined probably represented individuals from very 

 different epochs. 



Among mammals the Orang seems to exhibit an unusual ten- 

 dency to variation, and a series of crania of this animal shows 

 many individual peculiarities. 



Doubtless these are shown by other portions of the skeleton as 

 well, but, at the time a large series of Orangs was available, my 

 attention was directed almost entirely to the skull, and it can 

 only be said that this species has considerable range in point of 

 size, adult males being from four feet to four feet eight inches in 

 height. 



The Orang is a striking example of the cranial changes brought 

 about by age, these being so great that four species have been 

 founded on characters which a sufficient number of specimens 

 shows to be due to age alone. 



Apart from these it may be said that the foramen magnum has 

 hardly the same shape in any two skulls, while the nasals vary 

 as much, being sometimes long and narrow, sometimes short 

 and broad, and in one case quite absent. 



The shape and size of the orbits is very variable and they may 

 be close together or some little distance apart. At the same time 

 the supra-orbital ridges are often larger in rather young Orangs 

 than in very old individuals. 



A rather curious feature in the Orang is the tendency to de- 

 velop an extra molar, the normal number being three, as in man. 

 Usually this additional tooth is in the lower jaw and unpaired, 

 but one jaw possessed four perfect molars on either side. 



Our Mule Deer shows great cranial variability, both in size and 

 proportions, and while typical skulls of the Mule Deer, the Co- 

 lumbia Deer, and Virginia Deer may be i-ecognized at a glance, in 

 many instances, where the antlers have been shed it requires care- 

 ful examination to distinguish the skulls of the species apart. 



The tendency to develop an extra pair of ribs is not very un- 

 common among birds, and, as we know, is occassionally seen in 

 mammals, where it may take the form of a short pair of ribs on 

 what would normally be the first lumbar, much more rarely a rib, 

 or pair of ribs, on the seventh cervical, and sometimes that of an 

 unpaired rib on the first lumbar. 



In cases of this last mentioned variant the odd rib is usually 

 longer than when an extra pair of ribs is present. 



The true sacrals of birds are ordinarily devoid of parapophyses, 

 in fact this is one of their distinguishing characteristics, yet among 

 Cormorants these processes are not infrequently present and I have 

 once observed them in a Goatsucker. 



Although it is not uncommon to meet with an additional pair 

 of ribs among birds, any lessening of the normal number is very 

 rare and only once has such a case come under my notice, this 



