16 THE STUDY OF PLANTS IN ANCIENT AND MODERN TIMES. 
a plant do, it is true, take one back as far as Aristotle and his school; but the ideas 
of vegetable life entertained at that time are scarcely more than fantastic dreams; 
and the recognition now accorded to them springs rather from a reverence for 
antiquity than from any intrinsic merit which they possessed. The first experi- 
mental investigations into the vital phenomena of plants were published by 
Stephen Hales in 1718; but it was not till a hundred years later that this kind 
of research really came into vogue. It brought with it the conception of a cell 
as a miniature chemical laboratory, and looked for mechanical interpretations of 
the phenomena of nutrition, sap-circulation, growth, movement—in short, all vital 
processes—and for some connection between these processes and the external form. 
Whereas, in the case of descriptive and speculative botany, and in the study of 
development, the entire plant was first taken into consideration, next its several 
parts, and lastly the cells and protoplasm; in the new department of inquiry, on 
the contrary, the complete histories of the ultimate organs were studied first 
of all, then the significance of the different forms of the several members, and lastly 
the phenomena occasioned by the aggregate life of all the various kinds of animals 
and plants. 
Modern science, governed as it is by the desire to lay bare the causes of all 
phenomena, is no longer satisfied with knowledge concerning the existence of cells, 
the arrangement of the different forms of cell, the development of their contents, 
and the changes undergone by cell-membranes. At the present day we inquire 
what are the functions of the various bodies which are formed within the proto- 
plasm? Why is the cell-membrane thickened at a particular spot in a particular 
manner? What is the meaning of all the tubes and passages which exhibit such 
great diversity of size and shape? What part is played by the peculiar mouths of 
these channels, and why do they vary so greatly in shape and distribution in plants 
which are subject to different external conditions? We are no longer content to 
determine in what manner the rudimentary organ of a plant is produced, or how 
it expands in one case and frequently divides, or else is arrested in its growth and 
shrivels up; but we inquire the reason why one rudiment grows and develops 
whilst another is obliterated. For us no fact is without significance. Our 
curiosity extends to the shape, size, and direction of the roots; to the configuration, 
venation, and insertion of the leaves; to the structure and colour of the flowers; 
and to the form of the fruit and seeds; and we assume that even each thorn, 
prickle, or hair has a definite function to fulfil But efforts are also made to 
explain the mutual relations of the different organs of a plant, and the relations 
between different species of plants which grow together. Lastly, this department 
of research (the rapid growth of which is due to Darwin) includes amongst its 
objects a solution of the problem of the ultimate grounds of morphological variety, 
the causes of which can only be sought for in a qualitative variation of protoplasm. 
Specific relationship is explained by attributing it to similarity in the constitution 
of the protoplasm of allied species, and the affinities exhibited by living and extinct 
plants are used as means of unfolding the hereditary connection between the 
