LECTURE XXX. 



CAUSAL RELATIONS OF GROWTH OF THE DIFFERENT ORGANS 

 OF THE PLANT ONE TO ANOTHER. 



(CORRELATIONS.) 



The processes of growth described in the last four lectures must for the time 

 being be taken simply as facts, the determination of the causes of which is at present 

 impossible. That the embryonic rudiments of all organs proceed from growing- 

 points, which are themselves remains or continuations of the fertilised oosphere of 

 the embryo, that in these the differentiation of the embryonic tissue takes place, that in 

 post-embryonic development they not only increase in size, but also only attain their 

 permanent outward form during this period of growth, and so forth — all these matters 

 of growth appertaining to the development must in the meantime be taken as facts : 

 that is, we must be satisfied meanwhile to look upon the phenomena in question 

 as purely objective, and free from preconceived ideas, in order to obtain subse- 

 quently a glimpse into the causes which bring it about that things go on as they 

 have been described, and as direct observation shows. Vegetable physiology finds 

 itself with respect to these phenomena of growth in the same position as is crystallo- 

 graphy, for instance, respecting the question why common salt, the diamond, copper, 

 &c., in spite of their differences in other respects, crystallise in the regular system, 

 whereas graphite, calc-spar, quartz, &c. assume forms belonging to the hexagonal 

 system. 



Nevertheless, in our considerations on growth so far, we have already obtained 

 here and there glimpses of causal relations by the way. With respect to cell- 

 formation in the growing-points, the law of the rectangular intersection of cell-walls 

 presented to us a causal element from which we were able to make intelligible 

 the arrangement of the cells in the most different embryonic tissues: in the same 

 way we found in the radial or dorsi-ventral structure of the growing-point the most 

 immediate cause for the fact of the organs being placed vertically, obliquely, or 

 horizontally, and producing their outgrowths on all sides, or only on one side, and 

 so forth. Evidently there lie in these relations, at least the beginnings of a causal 

 understanding of the matter, although we are by no means in a position to follow 

 causes and effects step by step according to current mechanical conceptions. 



In this and the following lectures we shall be concerned with those phenomena of 

 growth in which the effective causes or the causal principle are more clearl)' manifested, 



