Mar., 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



49 



birds from his correspondents at Seville. The South 

 American and European cousins made friends at once, 

 and formed a united flock, amongst which it was hardly 

 possible to discriminate the two species, so much alike 

 are they except in the height of the breeding season. 



In the spring of 1895 the Ibises showed signs of 

 breeding, and were to be seen carrying about sticks in 

 their beaks. Many pairs were soon formed, without 

 regard as to both sexes belonging to the same variety. 

 The nests were placed on the summits of the stunted 

 trees in the Great Aviary, formed of sticks, straw, moss, 

 and other materials supplied to the birds bv the keepers. 

 The first brood of three young ones was hatched on 

 June 19th of that year. Since that period the same 

 process has been repeated every season, and though 

 there have been many accidents and misadventures to 

 these birds, which have a difficult task to hold their 

 own amongst so many evilly-disposed neighbours, the 

 flock of Glossy Ibises still exists, and the birds go on 

 breeding, with more or less success, every year. It is 

 impossible to tell the exact parentage of the different 

 birds now in the Society's Gardens, but the greater 

 number of them are probably hybrids between Plegadis 

 falcinellus of Europe and P. guarauna of Argentina. 



A new consignment of the European species has 

 lately arrived, which, when the breeding-season of 1905 

 comes on, will, no doubt, give fresh vigour to this 

 most interesting family. 



Heredity. 



By J. C. Shenstone, F.L.S. 



II. 

 Sprengel, in his great work, led to the knowledge 

 that forms of flowers exist solely for the purpose of 

 securing the fertilisation of the seed. Those flowers 

 which are inconspicuous and do not attract insects 

 by their perfume or by their honey, as for instance 

 most of the grasses, discharge clouds of pollen into 

 the air, which is conveyed by the wind to other plants; 

 but in the majority of cases flowers are specially con- 

 structed to attract insects in search of honey and of 

 this pollen, as the yellow dust is now called. In their 

 search they convey portions of the pollen from flower 

 to flower, and thus the seeds of one plant are usually 

 fertilised by pollen conveyed from another. Sprengel 

 did not realise the full importance of the cross-fertilis- 

 ation thus secured, but no botanist now doubts that 

 cross-fertilisation is a profound necessity, and that 

 the innumerable forms of flowers and their brilliant 

 colours are due to their being constructed to attract 

 the attention of insects. Sprengel, like many other 

 great men, was born too soon. 



Darwin's great work in establishing the theory of 

 Evolution, and in demonstrating that we owe the in- 

 numerable forms of animal and vegetable life to a 

 process of development, and to a process of " natural 

 selection " — those individuals least suited to their en- 

 vironment disappearing as the result of the fierce com- 

 petition constantly proceeding in nature — is too well 

 known to need repetition here, but I should explain 

 that whilst Chas. Darwin was elaborating his theory, 

 and immediately afterwards, a mass of work was 

 done by others which contributed to place the new 

 development of knowledge upon a sure foundation. 

 Not least among those who helped in this work was 



Nageli, who attacked the problems of life from quite 

 a different direction, bringing a considerable training 

 in physical enquiry to bear upon the study of the 

 development of plants by the aid of the microscope. 



If a very thin slice of the pith from a young shoot 

 of, elder be examined under the microscope, it will be 

 seen to consist of a number of small bladders known 

 to botanists as cells. When a cell is subjected to a 

 temperature of 122 F. its contents shrink away from 

 the outer skin, and can be discovered to consist mainly 

 of a viscid granular substance. Nageli showed that 

 this was true of the cells of the most lowly as well as 

 the most highly developed plant and animal, for both 

 of these are entirely composed of such bodies, and that 

 everything living has grown from a single cell by a 

 process of division, each cell becoming divided into two 

 or more perfect cells, which are seen to divide again and 

 again during the life of the tissue. Nageli also en- 

 riched the theory of evolution, as afterwards acknow- 

 ledged by Chas. Darwin, by establishing the fact that 

 there exist laws of variation in living things, which 

 lead to their perfection, and also to their variation 

 independently of the changes brought about by the 

 struggle for existence. Thus at the end of the last 

 century it was admitted that the essential basis of 

 animal and vegetable life lies in the granular sub- 

 stance contained within the cell; that each animal 

 and each plant is developed from a single cell now 

 called the germ-cell\ and that whilst the chemical and 

 physical forces acting in living things are indistin- 

 guishable from the same forces when acting in dead 

 matter, there exist indications of yet other laws of 

 variation which lead to the perfection of living forms 

 and to their difl'erentiation. Finally, that the innumer- 

 able forms of plants and animals existing to-day are 

 the outcome of natural selection; that these are due 

 to the survival of those most suited to the changing 

 conditions of life, and to the destruction of forms less 

 able to hold their own in the struggle for existence.* 



We are all familiar with the stages through which 

 some members of the animal kingdom, e.g., butter- 

 flics and moths, pa.ss during their development into 

 the perfect form, k caterpillar is hatched from an 

 &iCZ^ this in due course is transformed into a chrysalis, 

 from which the perfect butterfly or moth emerges, and 

 the frog passes tlirough the tadpole stage before ar- 

 riving at complete development. Some classes of 

 plants pass through similar .stages, and it is held by 

 most naturalists that the history of each individual 

 recapitulates the history of its ancestry, and that if 

 we traced the development of an animal or a plant 

 from a single cell, or minute viscid bodv from which 

 each individual is developed, we should discover the 

 leading features of its ancestry. 



After Darwin's theory had .secured the support^ of 

 men of .science, Weismann impressed upon us the im- 

 portance of the fact that all the characters, including 

 the most minute peculiarity of bodily structure or 

 mental disposition, must be transmitted from genera- 



•It is contended by some botanists that species may liave come 

 into existence suddenly. The variations in both plants and 

 animals, popularly known as sports, are known to all observers 01 

 nature. The varieity of clover with four leaflets instead of three, 

 and human beings with an abnormal number °« fin-ers or toes 

 serve as examples. It is contended that such variations, called by 

 biologis's mutations or discontinuous variations, may have given 

 rise tS new species. Gardeners and breeders o f an.nials h aye taken 

 advantage of such variations for producing cultivated va^eties, but 

 no variety obtained in this manner has so far proved capable ot 

 holding its own in its wild state. 



