OP GROWTH. 467 



We owe many thanks to Nageli for some communications contain- 

 ing very able observations (Zeitschrift fur wissenschaftliche Botanik, 

 Pt. I.). The writings of K. Miiller, in the Botanische Zeitung, are 

 also valuable ; and in the labours of Hartig, and other such, we recognise 

 pleasing signs of a better time, though with some of the results which 

 Hartig supposes he has obtained I cannot agree. 



The doctrine of the formation of cells is treated of 14. 



188. It has not yet been discovered how far the various parts 

 of plants, or the various groups of plants, present various kinds of 

 growth. Accurate investigations are wanting on this subject. So 

 far as this condition influences the form, or the change of form, in 

 plants, it has been already treated of in Morphology. 



In the animal kingdom the phenomena of reproduction and 

 growth stand in close connection. Under the term reproduction, 

 used in this sense, is to be understood a new formation to supply 

 a part that has been lost, in the same place, and of the same form. 

 There is, probably, no such reproduction in the vegetable kingdom. 

 A part of a plant which is lost is not restored by the repro- 

 duction of a corresponding member; but, on the contrary, the 

 process of the healing of wounds from loss of substance takes 

 place frequently by the filling up of the existing breach with a 

 substance similar to cork. 



Of the varieties of the processes of vegetation in various plants, or 

 parts of plants, we have at the present moment nothing to say. I have 

 already, in speaking of the formation of the pollen, called attention to the 

 opinion of Nageli. The special parent-cell is always formed in the 

 interior of another cell ; but this mode of formation is different from 

 that earlier described. Nageli found it frequent in the Algce. 



Respecting the peculiar chemical processes of individual groups of 

 plants, we know nothing. In the indefinite growth of the entirely inde- 

 pendent individuality of the plant there can be no reproduction in the 

 same sense as the reproduction of the tail of a lizard, &c. ; for the indi- 

 vidual embraces a definite circle of forms, but not a definite number of 

 forms, and never produces all its essential organs at the same time : so 

 that the loss of a member may be replaced in a plant, but it cannot be 

 through the restoration of the same form in the spot from whence it was 

 removed, but by the formation of a similar organ in another place. The 

 loss of certain organs in plants, and the formation of corresponding 

 organs in other places, is quite conformable with the general laws of 

 vegetation, of which we have earlier spoken. The tree, for instance, 

 that loses its leaves in autumn, forms new leaves in spring from its buds ; 

 but each bud is an essentially new individual, which consists of perfectly- 

 formed stem and leaves; but it is developed upon the remains of a 

 former individual, and is vitally united to it. Internodes that have lost 

 their leaves never throw forth new leaves, which grow rather on new 

 internodes, and thus belong to a new individual. But two examples 

 have as yet come to my knowledge wherein there has appeared to be 

 a reproduction in the same place of one and the same part which had 

 been lost. One of these occurred in a plant belonging to the family of 



ii H 2 



