THE STUDY OF PLANTS IN ANCIENT AND MODERN TIMES. 15 



had indeed already been displaced by another method of classification, that of the 

 French observers Jussieu (1789) and De Candolle (1813), who framed systems said 

 to be natural when contrasted with the artificial system of Linnseus. At bottom, 

 however, these classifications only differed from the Linnaean in the fact that they 

 multiplied and widened the grounds of division. The main division of Phanero- 

 gamia into those which put forth one cotyledon (or seed-leaf) on germinating 

 (Monocotyledones) and those whose seedlings bear two cotyledons (Dicotyledones) 

 is the only one that could serve as a starting-point for a system based on the history 

 of development; but when we come to the grouping of Dicotyledones into those 

 destitute of corolla (Apetalse), those with the corolla composed of coherent petals 

 (Monopetalse), and those with the corolla composed of distinct petals (Dialy- 

 petalse), we have already to admit something forced, and a reliance on characteristics 

 merely external. 



The system which is the outcome of the study of development starts with 

 the idea that similarity between adult forms is not always decisive evidence of 

 their belonging to the same group, and that the relationships of different plants 

 is much more surely indicated by the fact of their exhibiting the same laws of 

 growth and the same phenomena of reproduction. Plants exhibiting widely 

 different external forms in the mature state are nevertheless to be looked upon 

 as closely allied if they are constructed according to the same plan, and vice versa. 

 There can be no question that a system based on these principles means a material 

 advance. At the same time it cannot be overlooked that great difficulties are 

 involved in hitting upon the right selection from among the number of phenomena 

 observed in the course of a plant's development, and in determining which of these 

 phenomena are to be referred to a mode of construction common to a number 

 of plants, and therefore treated as fundamental properties, and which should be 

 esteemed merely as outcomes of the conditions of life affecting the existence of the 

 plant in question. 



OBJECTS OF BOTANICAL KESEAECH AT THE PRESENT DAY. 



DESCRIPTIVE BOTANY only concerns itself with the configuration of a plant. 

 COMPARATIVE MORPHOLOGY endeavours to trace back to a single prototype the 

 extremely various forms exhibited by mature plants. The history of development 

 deals with the growth and differentiation of such forms. But all these paths of 

 research shirk the problem of the biological significance of the different forms. 

 The line of investigation starting from the conception of a plant's life as a series 

 of physical and chemical processes, and which attempts to elucidate the configura- 

 tion of a plant in the light of its environment, could not be developed with the 

 slightest prospect of success until physics, chemistry, and other allied sciences had 

 reached a high degree of perfection, and till botanists had become convinced that the 

 phenomena of life are only to be fathomed by means of experiment. 



The earliest attempts to define the biological significance of the several parts of 



