52 



KNOWLEDGE 



[March 2, 1891. 



estimated from experiments on the diffusion and ^^scosity 

 of gases. One of the most striking illustrations in the 

 book is given in the chapter describing Sprengel pumps 

 and high vacua. He says, " These high exhaustions are 

 called by coui-tesy vacua, as they are the nearest approaches 

 that physicists have been able to make to an absolute 

 vacuum by the most refined methods known to science ; 

 and yet we should hardly call that space a vacuum in 

 every cubic inch of which there are 350 million million 

 molecules of the gas ; and, according to the latest con- 

 clusions of the molecular theory, that is about the number 

 in a cubic inch of air when it is reduced to one-millionth 

 of the atmospheric pressure. To form some conception 

 of the vastness of this number, we may consider that if, 

 through the side of a little glass bulb of one cubic inch 

 capacity that had been exhausted to this extreme degree, 

 a hole were to be made through which a million molecules 

 could enter in every second, it would take ten years for 

 the pressure inside the bulb to be doubled ; that is, for as 

 many more molecules to pass through as those already 

 contained in the bulb." Unfortunately, the book does not 

 contain an index. 



Tlifi Crimiudl. By Havelock Ellis. (Walter Scott, 

 1890.) During the last fifteen years the study of criminal 

 anthropology has been carried on with great activity, and 

 the rich harvest of facts which has already been collected 

 is likely to lead to valuable conclusions, which may pro- 

 bably in the future enable us to deal more wisely with the 

 criminal residuum that will always exist m a civilised 

 society, in spite of school boards aud free libraries and the 

 other panaceas of certain theorists and philanthropists 

 which are constantly proclaimed, like the patent medi- 

 cines of the advertising quack, as a cure for all ills, social 

 and political. The sentimentalist, who generally sympa- 

 thises so much more with the notorious criminal than with 

 his poor neighbour or relation, wiU be surprised to read 

 what Mr. Havelock Elhs says about the physical sensi- 

 bility of the criminal classes. He instances the wide pre- 

 valence of tattooing among them, fi'equently of the most 

 sensitive parts, which are rarely tattooed amongst bar- 

 barous races, as showing the deficient sensibility of 

 criminals to pain. Lauvergne mentions a convict who 

 smiled with pleasure when, moxas having been applied to 

 him, he saw his skin bm-niug and heard it crack. Though 

 loud in their complaints of trivial ailments, thej- are often 

 unconscious of severe Ulness. At Chatham, in 1888, a 

 prisoner dropped down dead on returning from labom- ; 

 both lungs were foimd to be affected, and death was 

 probably due to syncope. He had made no complaints to 

 anyone. Prisoners will inflict severe injuries on them- 

 selves in order to gain some trifling object. At Chatham 

 in 1871-72, 811 voluntary wounds or contusions are 

 recorded ; 27 prisoners voluntarily fractured a hmb ; and 

 17 of them had to submit to amputation ; 62 tried to 

 mutilate themselves, and 101 produced woimds by means 

 of corrosive substances. 



BIRDS AND BERRIES. 



By the Kev. Alex. S. Wilsox, M.A., B.Sc. 



NATURAL History furnishes many curious illus- 

 trations of the mutual relationships subsisting 

 between the animal and vegetable kingdoms. 

 Of these we have remarkable examples in the 

 weU-known adajstations of flowers to the visits 

 of insects. It is of the highest importance to a plant to 

 have its seeds properly crossed, and this involves the 



transference of pollen from one flower to another of the 

 same species. Insects frequenting flowers get dusted 

 with this substance ; they carry it with them to other 

 flowers, where some of it adheres to the stigma prepared 

 for its reception. The honey is not provided merely to 

 gratify the bees, but as an inducement to them to visit 

 the flowers and effect their fertilisation. A flower, in fact, 

 is httle more than an apparatus for securing cross-fertili- 

 sation. The scent and colour serve to guide the insects, 

 while the shape of the flower is generally such that the 

 bee cannot reach the honey without effecting the object 

 for which it has been attracted. 



Insects are not, however, the only animals to which 

 plants are thus related. A considerable number of 

 flowers appear to be adapted to birds rather than to 

 insects. Humming-birds in America, sun-birds in Afiica 

 and India, the Malayan lories, and the Australian honey- 

 eaters, visit flowers and efiect cross-fertilisation very 

 much as butterflies and bees do in Europe. The bird- 

 fertilised class includes species of Fuchsia, Passiflora, 

 Salvia, Abutilon, Impatiens, Lobelia, Marcgravia, Ery- 

 thrina, and Cassia. Ornithophilous, or bird -fertilised, 

 flowers are generally of large size, tubular in form, and 

 secrete abundant nectar. Their colours are extremely 

 brilliant, scarlet being perhaps the most frequent. 

 Flowers of this description are rarely produced by her- 

 baceous plants ; they occur, as a rule, only on shrubs and 

 trees. 



Birds are employed to carry seeds much more frequently 

 than for the transport of pollen ; these bird-fertilised 

 flowers have, however, a special interest as throwing light 

 on the relations between birds and coloured fruits. 



Fruits and seeds constitute a large proportion of the 

 food of many animals ; but if any animal were systematic- 

 ally to consume the seeds of a particular plant, the latter 

 would run no small risk of extermination. To the animal 

 itself this would be a serious misfortune if thereby it 

 were deprived of its usual food. In the interest of the 

 plant, as well as of the animal supported by it, some 

 limitation to the consumption of seeds is necessary. 

 Hence many plants conceal their seeds ; in other cases 

 these are obscurely colom-ed or encased in hard shells in 

 order that at least some of them may escape being de- 

 voured. Other plants have been able to avail themselves 

 of the services of animals, and can thus reimburse them- 

 selves for the loss they occasion. In some parts of Africa 

 visited by the late Dr. Livingstone the grasses of the 

 pastures frequented by herds of antelopes had their seeds 

 adapted for dispersion by these animals. This arrange- 

 ment is a mutual benefit, for in disseminating the seeds 

 of the grass the antelopes imconsciously provide for their 

 own futm-e. The same thing may be said of birds which 

 feed on berries and other succulent fruits. These are 

 useful to plants in scattering their seeds, and in return 

 they receive the soft, sweet pulp of the fruit, with the 

 prospective advantage of a future crop from their own 

 sowing. In plants which employ birds for then- dis- 

 persion the adaptation is seen in the succulence, sweet 

 taste, and bright colour of the fruit ; and in the hardness, 

 bitter taste, and emetic or purgative properties of the 

 seed. There are two perfectly distinct objects to be 

 secured ; the attraction of the birds, and the protection of 

 the seeds. Hence the succulent portion is not as a rule 

 the seed itself, but some part of the pericarp or wall 

 of the fruit. Berries have the pericarp entirely succu- 

 lent, the hard seeds being embedded in pulp. Drupes, or 

 stone-fruits like the cherry, have only the outer layers 

 of the pericarp soft ; the inner wall of the fruit, called 

 the endocarp, is indm-ated, and forms the stone enclosing 



