66 • 



into roots, as not seldom occurring. At a time when the homology of 

 organs was the order of the day, such facts drew particular attention. 



For various reasons Beijerinck's phylogenetical considerations, 

 given at the conclusion of his elaborate treatise, are the most attract- 

 ive part of his paper. He treats therein the question as to how much 

 hght his observations throw upon the methods by which stem and root 

 of higher plants have evolved in the course of time. In the first place 

 he contrasts the two theories on the development of the stem: the 

 stem should be developed from the "Blattbasen", or the stem and the 

 leaf should be considered as homologous to a "thallus". 



The former conception was first carefully considered with referen- 

 ce to Goethe's Metamorphoselehre i), to a treatise by du Petit- 

 Thouars 2) and to that by Gaudichaud 3), It appears that Delpi- 

 No's work "Teoria generale della FiÜotassi" 4) which gave a special 

 elaboration of this conception, arrested Beijerinck's attention very 

 considerably ; undoubtedly the model which Beijerinck constructed 

 of the sphere-pile of Delpino, and which in later years he used to 

 demonstrate repeatedly, dates from this time. Beijerinck agrees 

 that the structure of the little sterns of mosses and of the young fern- 

 plants point toward the first hypothesis, and especially toward Del- 

 PiNo's elaboration of it. Yet he rejects this hypothesis, referring 

 among other things to C. de Candolle's observation of 1881 that the 

 youngest leaves at the vegetation-point show neither an arrangement 

 according to Delpino's "Blattstandsaule", nor a shifting, as ac- 

 cepted by Delpino, but that they appear from the first moment with 

 the final phyllotaxis. 



The second conception, the thallus theory, is more attractive to 

 Beijerinck, and he imagines that higher plants descend from "liver- 

 wort-like" ancestors. The often-occurring double-rowed phyllotaxis 

 reminds one of the bilateral thallus of such ancestors. Even in some 

 Orders of which most of the species show spiral-arrangements of the 

 leaves, some "thallous" species occur. Beijerinck believes that the 

 transition of the bilateral phyllotaxis into the spiral types which 

 should have occurred in phylogenesis during a later stage of develop- 

 ment of the stem, must be viewed in the light of the theory of Airy. 

 This investigator thought that such higher systems of phyllotaxes are 

 adaptations to the small space available for lateral organs in the 

 buds. Airy illustrated such a transition by fixing wooden balls to a 

 stretched rubber band, so as to make them conform to a double- 

 rowed arrangement of leaves at a stem, and then letting the band 

 contract, whereupon spiral arrangements actually occurred. 



1) J. W. VON GoETHE, Versuch über die Metamorphose der Pflanzen, Stuttgart 

 1831. 



2) R. DU Petit-Thouars, Essai sur la végétation considérée dans Ie développe- 

 ment des bourgeons, Paris 1809. 



3) C. Gaudichaud, Recherches gén. sur l'organographie, la physiologie et l'orga- 

 nogénie des végétaux, Mém. de l'Acad. des sciences; Paris 1841. 



*) Genua 1883. 



