64 • 



his own observations on the development of root-buds and the origin 

 of adventitious roots on different parts of the plant were described 

 therein with great care, and illustrated with 86 especially clear and 

 original drawings. To these observations were added the fairly 

 numerous cases which at that time had aheady been pubhshed in 

 botanical and horticultural hterature; the whole was made into an 

 outHne which included the entire plant kingdom. Any botanist 

 wishing to get some idea as to how the various plant families show the 

 above-mentioned peculiarities, must still have recourse to Beije- 

 rinck's treatise, now more than half a century old. Stronger still: any 

 modern biologist desirous of finding the general rule applicable to 

 the many diverse morphological phenomena, and who wishes to 

 completely understand the meaning of it, or who wishes to consider 

 the relation to other manifestations of life, will have his attention 

 held, on reading the introductory discussions and the still more ar- 

 resting concluding chapter. 



The leading motives, which in the first publication of 1882 were 

 stated with a certain reluctance, are emphasized in this more mature 

 treatise. The significance of adventitious organs for the study of 

 ontogenesis is one of them. One needs only to read the statement: 

 "manche Gründe sprechen für die Annahme, dass bei Knospen und 

 Wurzeln die namlichen Ursachen, welche ihre erste Entstehung ver- 

 anlassten, auch bei ihrem spateren Austreiben aus einer ruhenden 

 Anlage im Spiele sind". And is not a similar note struck by this thesis : 

 "Die Art und Weise, wie diese Krafte dabei arbeiten, ist gewiss auf 

 dem Geblete der Reize zu Hause, und viele Gründe sprechen für die 

 Annahme, dass die ganze Ontogenie auf Nahrungsreizen beruht" ? 



Another Leitmotiv which may be heard repeatedly is the sig- 

 nificance of the "transport of matter" for the determination of the 

 place where adventitious growth will occur. 



Where the rising sap-stream in the xylem undergoes a change of 

 direction, as a result of encountering specialised structures of the 

 tissue — in undamaged vegetation-points, at the top ends of 

 stems or roots, in axils, at the vertices of the branchings of the leaf- 

 veins, and at the points of origin of the rootlets — there are to be 

 found the places which preferably produce adventitious buds, ac- 

 cording to Beijerinck. 



On the other hand, the points where the plastic nourishment ac- 

 cumulates, or where its movement is retarded or hindered, are 

 preferred for the appearance of adventitious roots. In both cases — 

 as Beijerinck points out — one can hardly imagine a more appropri- 

 ate arrangement, since the young buds, soon to become green and to 

 assimilate independently, must draw upon the water supply on 

 developing ; the adventitious roots, however, which may be compared 

 with colourless parasites, must be situated as f avourably as possible to 

 receive organic matter produced elsewhere. 



