BOTANY 



of the whole problem of organic evolution, that the. belief in the 

 immutability of species was finally destroyed. From the study of the 

 fossil remains and impressions of animals and plants it has been 

 established that in earlier geological periods forms of life differing from 

 those of the present age existed on the earth. It is also generally 

 assumed that all living animals and plants have been derived by 

 gradual modification from previously existing forms. This leads to 

 the further conclusion that those organisms possessing closely similar 

 structure, which are united as species in a genus, are in reality related 

 to one another. It is also probable that the union of corresponding 

 genera into one family and of families into higher groups in a 

 "natural" system serves to give expression to a real relationship 

 existing between them. The evolutionary developments, i.e. the 

 transformations which an organism has undergone in its past generations, 

 were termed its PHYLOGENY by ERNST HAECKEL( 2 ). The develop- 

 ment or series of changes passed through by the individual in attaining 

 the adult condition he distinguished as the ONTOGENY. It is assumed 

 on the theory of descent that the more highly organised plants and 

 animals had their phylogenetic origin in forms which perhaps 

 resembled the simplest still existing. The phylogenetic development 

 proceeded from these, on the one hand in the direction of the higher 

 animals, and on the other in the direction of well-defined plants. On 

 this assumption, which is supported by the properties which animals 

 and plants have in common and by the impossibility of drawing a sharp 

 line between animal and plant in the lowest groups, all living beings 

 form one NATURAL KINGDOM. 



The following may be mentioned as distinctly marked character- 

 istics of plants. The external development of the important surface of 

 the body, which serves to absorb the food in plants, contrasts with the 

 internal body surface to which the mouth gives entrance in the 

 animal. The investing walls of vegetable cells are already represented 

 in certain series of lower organisms which afford the probable starting- 

 point for the phylogenetic development of plants. Lastly, the green 

 chromatophores of plant-cells are characteristic. By means of the 

 green colouring matter, plants have the power of producing their own 

 nutritive substances from certain constituents of the air and water, 

 and from the salts contained in the soil, and are thus able to exist 

 independently ; while animals are dependent, directly or indirectly, 

 for their nourishment, and so for their very existence, on plants. 

 Almost all the other differences which distinguish plants from animals 

 may be traced to the manner in which they obtain their food. 

 Another characteristic of plants is the unlimited duration of their 

 ontogenetic development, which is continuous at the growing points 

 during their whole life. That none of these criteria are alone 

 sufficient for distinguishing plants from animals is evident from the 

 fact that all the Fungi are devoid of green pigment, and, like animals, 



