BOTANY 141 



ble for the adult characters of the future adult, even at the time when they are lurking 

 within the confines of a single germ cell. Thus the difference between a " graft-hybrid " 

 and a genuine hybrid is fundamental; the one depends on an accidental coalescence, as 

 it were, of specifically distinct individuals, whilst the other owes its origin to the min- 

 gling of the parental characters in the germ cell from which it sprang. The example of 

 Winkler's Solatium Darwinanurn (hybrid) however may prove to be an example of. a 

 vegetative fusion of the nuclei of stock and scion since the number of its nuclear chro- 

 mosomes is intermediate between those of the two parent plants. 



See Baur, E. Einfiihrung in die experimented vererbungslehre (Berlin, 191 1), a good account 

 of the subject of graft-hybrids and also of other developments in genetic science; H. \Vinkler, 

 1907, Ueber Propfbastarde v. Pfianzliche Chimaren (Ber. d. Deutsch. Bot. Gescllsch., Bd. 

 xxv). Winkler has published a number of more recent papers, and his larger work entitled 

 Untersuchungen ueber Propfbastarde is in course of publication by G. Fischer, Jena. 



Ecology. Another modern development of botany, ecology, consists in the endeav- 

 our not only to systematise the older " Natural History." observations, but to utilise 

 and extend them so as to throw light on the causes which underlie and determine the 

 grouping and mode of distribution of the plants within a given area. This study is be- 

 ing prosecuted with vigour, especially in Great Britain, and in America. So far as the 

 former country is concerned the recent work has been brought together in A. G. Tans- 

 ley's Types of British Vegetation. A considerable amount of experimental work has also 

 been undertaken with the object of unravelling the relation between the plant and its 

 surrounding, especially the soil conditions. Perhaps the most important of these 

 results consists in the recognition of the importance of the physical and physico-chemical 

 factors involved. The determination of the " wilting coefficient " by Briggs and 

 Shantz has thrown light on the question of water availability of different soils. The 

 percentage of moisture in the soil which is just below what was required to maintain 

 the turgidity of the plant (" wilting coefficient ") varies definitely in different classes of 

 soil according to its physical state of aggregation. This has of course long been known. 

 They ascertained that if samples of these different soils, saturated with water, are placed 

 in a centrifugal machine and the speed is so arranged as to exert a centrifugal force of 

 1,000 g, that the percentage of water which they respectively retain (." moisture equiva- 

 lent ") by virtue of absorption or surface tension, stands in a practically constant rela- 

 tion to the wilting coefficient, and they express this numerically by stating that within 



wilting coefficient 



a very small margin of error, the ratio : r ; = 1.84. 



moisture equivalent 



The ecological causes which determine the distributions of plants are not only physi- 

 cal but biological and are still for the most part obscure. Investigations, both in Eng- 

 land and especially in Canada, have shown that grass is injurious to young apple trees, 

 but a satisfactory and complete explanation of this has not so far been given. Indeed 

 the mutual reactions of organisms provides a field for investigation as yet largely open. 



Many of the supposed examples of symbiosis between plants and animals (e.g. ants) 

 have not stood the test of investigation. In the pitchers of nepenthes Jensen found liv- 

 ing larvae of 9 species of insects which pass their laval period. in these receptacles. They 

 contain " anti-ferments," which render them immune .to the action of the nepenthes 

 digestive ferment, apparently in much the same way as intestinal worms escape diges- 

 tion in the gut of their animal hosts, In such an example of course the grubs are utilis- 

 ing for their own purposes the animal food which, collected in the pitchers, would after 

 digestion otherwise have become available for the plant. 



See Briggs and Shantz, two papers on "Wilting Coefficient" In The Botanical Gazette, 

 vol. liii, 1912; A. G. Tansley, Types of British Vegetation, Cambridge, 1911; A. D. Hall and 

 E. J. Russell, Agriculture and Soils of Kent, Surrey and Sussex, Board of Agriculture & Fisheries, 

 London, 1911. 



Cytology. -One of the outstanding results of cytological research which has stood 

 the test of criticism consists in the recognition of the importance of the chromosomes. 

 These bodies are commonly very constant, both in form and in number for a given 



