14 THE STUDY OF PLANTS IN ANCIENT AND MODERN TIMES. 



course, and that accordingly every species is constructed on a plan fixed within 

 general limits and exhibiting variation in externals only. These, it is true, are often 

 more conspicuous at first sight than the direction and disposition of the parts which 

 are really fundamental, and secure the stability of the entire structure. But in 

 order to ascertain the plan of construction it was found necessary to go back to the 

 very first visible appearance of each organ; to determine how the original rudi- 

 ments of the embryo and the beginnings of roots, stems, leaves, and parts of the 

 flower are formed, and to see what rudiments succeed in opening out, branching and 

 dividing, and what remain behind to perish and be displaced by organs growing 

 vigorously in close proximity to them. 



These researches into the course of development of the separate parts of flower- 

 ing plants, and to a still greater extent the observations of the development of 

 cryptogams or spore-plants (rendered possible by improvements in the construction 

 of microscopes), led naturally to a study of the history of the elementary structures 

 of which all plants are composed. Previously three kinds of elementary organs had 

 been supposed to exist, utricles, vessels, and fibres. The observations of Brown and 

 Mohl (1830-1840) resulted, however, in the identification of the cell as the common 

 starting-point of all these elementary organs. This led to the further discoveries 

 that protoplasm is the formative and living part of a cell, and that each cell is 

 differentiated into a protoplasmic cell-body and a cell-membrane. It followed 

 that the envelope of the protoplasmic body, the cell-membrane, which had hitherto 

 been considered the primary formation, was in reality a product of the protoplasm 

 enveloped by it, and this discovery resulted in a complete revolution in the con- 

 ception of cells generally. Further investigation led to the conclusion that the 

 various modes of growth and multiplication depend on definite laws. That even 

 in the mode of juxtaposition of daughter-cells arising in reproduction, a certain plan 

 of construction may be distinguished in each species which must stand ultimately 

 in some oausal relation to the structural system of the whole plant. The progress 

 achieved along these lines in the course of a few decades has been extraordinarily 

 great, no doubt due to the peculiar fascination which the study of the life-histories 

 and transformations of living organisms and the observation of mysterious process* 

 invisible to the naked eye have had for the mind of the inquirer. 



In that group of plants which includes the forms classed together by the earli( 

 botanists under the name of Cryptogamia an altogether new world was revealec 

 An undreamed-of variety was discovered to exist in the processes of propagatioi 

 and rejuvenescence of these forms of plants by means of single cells or spoi 

 Objects which, having regard to their external form, had been assigned to widely 

 different groups, were found to be connected with one another as stages in the 

 development of one and the same species; and one result of these discoveries was 

 the establishment in this division of the vegetable kingdom of an entirely new 

 system of classification based on life-histories. The systematic arrangement of 

 Flowering-plants or Phanerogams also underwent essential alteration. The Linnsean 

 system, founded on the numerical relations between the different parts of the flower, 



