TRANSACTIONS OF SECTION K. 929 



explanation of what he means by ' turgor ; ' and the term is frequently used by 

 writers in the first half of the century in the same vague way. Some progress was 

 made in consequence of the discovery of osmosis by Dutrochet (1828), and more 

 especially by his observation (1837) that the movements of Mimosa are dependent 

 on the presence of oxygen, and are therefore vital. But it was not, and could not 

 be, until the existence of living protoplasm in the cells of plants was realised, and 

 the movements of free-swimming organisms and naked reproductive cells had 

 become more familiar, that the true nature of the mechanism began to be under- 

 stood ; and then we find Cohn saying, as long ago as 1860, that ' the living 

 protoplasmic substance is the essentially contractile portion of the cell.' This state- 

 ment may, perhaps, seem to put the case too bluntly and to savour too much of 

 animal analogy ; but the study of the conditions of turgidity has shown more and 

 more clearly that the protoplasm is the predominant factor. The protoplasm of 

 plantr-cells is undoubtedly capable of rapid molecular changes, which alter its 

 physical properties, more particularly its permeability to the cell-sap. It may be 

 that these changes cannot be directly compared with those going on in animal 

 muscle ; but if we use the term ' contractility ' in its wider sense, as indicating a 

 general property of which muscular contraction is a special case, then Cohn's 

 statement is fully justified. This is borne out by the observations of Sir J. Burdon- 

 Sanderson (18S2-8S) on the electrical changes taking place in the stimulated leaf 

 o{ Dioncea, and by Kunkel's (1878) corresponding observations on Mimosa pudica: 

 in both cases the electrical changes were found to be essentially the same as those 

 observable on the stimulation of muscle. AVe find, then, that the advances in 

 Physiology, like those in Anatomy, teach the essential unity of life in all living 

 things, whether we call them animals or plants. 



With this in our minds we may go on to consider in conclusion, and very 

 briefly, that department of physiological study which is known as the Bionomics 

 or (Ecology of plants. In the earlier part of the century this subject was studied 

 more especially with regard to the distribution of plants, and their relation to soil 

 and climate : but since the publication of the ' Origin of Species ' the purview has 

 been greatly extended. It then became necessary to study the relation of plants, 

 not only to inorganic conditions, but to each other and to animals ; in a word, to 

 study all the adaptations of the plant with reference to the struggle for existence. 

 The result has been the accumulation of a vast amount of most interesting infor- 

 mation. For instance, we are now fairly well acquainted with the adaptations of 

 water-plants (hydrophytes) on the one hand and of desert-plants (xerophytes) on 

 the other ; with the adaptations of shade-plants and of those growing in full sun, 

 especially as regards the protection of the chlorophyll. We have learned a great 

 deal as to the relations of plants to each other, such as the peculiarities of parasites, 

 epiphytes, and climbing plants, and as to those singular symbioses (Mycorhiza) of 

 the higher plants with Fungi which have been found to be characteristic of sapro- 

 phytes. Then, again, as to the relations between plants and animals : the adaptation 

 of flowers to attract the visits of insects, first discovered by Spreugel (1793), has 

 been widely studied ; the protection of the plant against the attacks of animals, 

 by means of thorns and spines on the surface, as also by the formation in its 

 tissues of poisonous or distasteful substances, and even by the hiring of an army 

 of mercenaries in the form of ants, has been elucidated ; and finally those cases 

 in which the plant turns the tables upon the animal, and captures and digests 

 him, are now fully understood. 



Conclusion. 



Imperfect as is the sketch which I have now completed, it will, I think, suiBce 

 to show how remarkable has been the progress of the science during the 

 nineteenth century, more particularly the latter part of it, and how multifarious 

 are the directions in which it has developed. In fact Botany can no longer be 

 regarded as a single science: it has grown and branched into a congeries of 

 sciences. And as we botanists regard with complacency the flourishing condition 



1900. 3 



