246 



KNOWLEDGE 



[November 1, 1890 



like those of oxen, and that they proved equally effective 

 weapons of defence. 



The structure of the teeth is somewhat similar to that 

 obtaining in the Iguanodon, but each tooth has two dis- 

 tinct roots. As in the latter, the extremity of the lower 

 jaw is devoid of teeth, and likewise has a separate terminal 

 bone. The upper jaw is, however, quite peculiar in ha\Tng 

 a distinct toothless bone at the extremity of the muzzle ; 

 so that it would seem probable that the mouth of these 

 reptiles formed a kind of beak sheathed in horn like that 

 of a tortoise. In young individuals the front horn-core is 

 a separate ossification, but in the adult it became firmly 

 united to the underlying bones, so that in this respect we 

 have a precise analogy with the horn-cores of the girafl'e. 

 The brain of the creature is very minute — relatively 



uncouth reptiles, of all shapes and sizes, while the air was 

 tenanted by the weird Flying Dragons, of which we have 

 treated in a previous article. 



Fiy. !i. — Side View of the Skull of a Hokned Dixosalk. 

 ^ nat. size, a, nostril ; b, eye ; hh', horn-cores ; r, upper part 

 of beak ; /), lower part of beak. (Afier Marsh.) 



smaller, indeed, than in any known Vertebrate ; this, 

 however, might have been expected from the diminutive 

 size of the brain in other Dinosaurs, since, in the same 

 groups, large animals always have relatively smaller brains 

 than then- smaller aUies. 



The pelvis of the Horned Dinosaurs is quite unhke that 

 of any members of the group ; the pubis being constructed 

 on the plan of that of the Iguanodon, but with the loss of 

 the bar running backwards parallel with the ischimn. It 

 thus results that the pubis is represented only by an 

 exaggeration of the process marked p. in the pelvis of the 

 Kiwi ; this process occupnng the same portion as the pubis 

 of the Megalosam* (Fig. 6), but not corresponding to it, 

 since that pubis represents the backwardly-directed bar of 

 the pubis of the Iguanodon. This assumption of the same 

 function and position by a totally difl'erent bone is a very 

 remarkable, although not an unique feature, and indi- 

 cates the extreme specialisation of its owner. 



With this brief reference to the Homed Dinosaurs, we 

 close om- survey of the Giant Land Reptiles. In a short 

 sketch Uke the present it is, of course, quite impossible 

 to do more than glance at a few of the more striking 

 features of the organisation of these most extraordinary 

 creatures. The reader who has followed us throughout 

 win, however, have acquired some general idea of their 

 chief peculiarities and affinities ; and he may profitably 

 endeavour to reaUse in his mind's eye the aspect of a 

 world in which the land- surface was peopled by these 



THE BREATHING ORGANS OF PLANTS. 



15y .1. rtNTLA.ND Smith, M.A., B.Sc. 



VEGETABLE organisms are composed originally of 

 one or more small spherical sacs called cells. 

 Each sac consists of a living mass of protoplasm 

 (TrpujTos, first and irX.a<rfia, form), or first formed 

 material, which has surrotmded itself with a wall 

 of cellulose, a substance of Uke composition to starch, but 

 which diSers fi-om starch in many important respects. The 

 primordial cells of the higher plants undergo many modi- 

 fications, which accord with the functions they have to 

 perform ; dinsion of labour induces change of form. Not 

 the least interesting of the modifications which they ex- 

 hibit are those which culminate in the production of the 

 breathing organs which form the subject of this paper. 



Scattered over the surface of all land plants are 

 numerous minute apertures, which, from the power they 

 possess of opening and closing, are termed stomatu (oro/ia , 

 a mouth). Not only do they occur on the leaves, the chief 

 assimilating organs of plants, but they appear in greater 

 or less numbers on yoimg stems and on the parts of the 

 flower, and may even be developed on the young under- 

 ground stem or tuber of the potato.* In fact, the only 

 portion of the plant on which stomata are not found is the 

 root ; the reason of this will soon appear sufiiciently 

 obvious. 



If the outer layer of sldn, or fpidrrmis (ctti, upon, and 

 Sepfxa, the skin), be peeled from ofi' the underside of a leaf, 

 and placed in a drop of water on a glass shde, with a 

 cover-slip laid over it, and then examined under a mode- 

 rately high power with a microscope, it wiU be found to be 

 pierced here and there with apertures large and small, the 

 size of which is determined by the species of plant from 

 which the epidermis has been derived. But a much 

 simpler method of proving the existence of these openings 

 in the skin-like structure is to place the cut end in water, 

 and to blow into the blade which has been inserted in the 

 mouth. Bubbles of gas will then apjjear at the cut end, 

 and will rise to the surface of the water. 



Illustrations of the lower epidermis of the leaves of five 

 s^jecies of plants treated as described above are shown in 

 Fig. 2, (I, h, c, (7, <■ ; their names are as foUows ; a, Hoya ; 

 h, Scolopendrium viilgare, the hart's tongue fern ; c, 

 LUium candidum, the white hly so much in request at 

 the present time in floral decorations ; (/, the cabbage, 

 Brassica oleracea, var. ; e, Iris. 



From calculations based on measiu'ements made on 150 

 difi'erent plants, the German botanist, A. Weiss, foimd 

 that the length of these stomata varied from -016 to -076 

 millimetres, the breadth from -016 to -079 millimetres, 

 and the area fi'om -00011 to -0019 millimetres. Substi- 

 tuting the British for the decimal system, we find that the 

 so-called breathing organs of plants exhibit lengths vary- 

 ing ajiproximately from j-^^^ to 3^3 inches, lengths of from 

 TsVa *o 31:2 inches, and superficial areas from 6256006 '^ 

 iTmmJo inches. They are found in millions on the sur- 

 face of plants ; as many as one hundred to two hvmdi'ed 

 are common numbers to find on one square miUimetre of 



* The potato, a staple article of diet, is a fleshily thickened 

 underground stem, whose cells are packed full of starch, and whose 

 eye.i are dormant buds. It is these buds which develop later on into 

 the potato stem which appears above ground 



