BOTANY PART i 



life of an organism is thus only possible when its construction is in 

 agreement with its environment, and it is ADAPTED TO THE CONDITIONS 

 OF LIFE. 



More penetrating morphological investigation soon shows that, 

 while almost every member of the plant body has its functions, 

 every peculiarity in construction cannot be regarded as adapted 

 to these functions or to the environment. This can only be said 

 of some of the characters of any part of the plant ; for example, the 

 abundance of the green pigment and the expanded form of foliage 

 leaves stand in relation to the main functions of the leaf. Such 

 characters are spoken of as useful to the organism. Many other 

 characters are indifferent, such as, for example, the nature of the 

 margin of leaves, described as entire, serrate, crenate, etc. Others 

 may even be unfavourable so long as they are compatible with life, 

 e.g. the absence of the green pigment from large portions of the leaf 

 in many cultivated forms of Sycamore. Many adaptations appear to 

 be less perfect than they could be. A character may be useful in one 

 species while it is indifferent or even harmful in another. Such facts 

 show clearly what care is requisite in judging of the significance of 

 organic forms and structures; it is no easy matter to prove such 

 assumptions by investigation ( 3 ). 



2. There is a second direction in which morphology endeavours 

 to attain a scientific understanding of the forms of plants. All 

 existing plants are regarded as genetically related, the most highly 

 organised with their diverse organs having gradually arisen phylo- 

 genetically from simple, unsegmented, unicellular forms. The 

 organism and its parts have thus undergone manifold transformations in 

 which, for example, particular organs by change of their structure 

 took over new functions or became adapted to new conditions of life. 

 It is thus a very important object of morphology to derive phylogenetic- 

 ally one form from another. Since the genetic development cannot 

 be directly traced but has to be inferred, morphology is dependent on 

 indirect methods in this problem. The most important indications 

 are obtained by the study of the ontogeny of organisms and by the 

 comparison of existing plants with one another and with those that 

 lived in preceding ages. Within certain limits the ontogeny often 

 repeats the phylogeny and thus contributes to the discovery of the 

 latter. Comparative study connects divergent forms by means of 

 intermediates. Since, however, the ontogeny never repeats the 

 phylogeny completely or without alterations, and the connecting forms 

 are often wanting, the results of morphology in this direction are 

 correspondingly imperfect. 



When the conviction has been reached after full investigation 

 that diversely formed members of the plant body had a common 

 phylogenetic origin, the hypothetical form from which we derive 

 them is termed the PRIMITIVE FORM, and the changes undergone by it 



