DORSIVENTRAL LATERAL SHOOTS 



95 



of the buds which will afterwards grow into a distichously-leaved shoot 

 shows that its phyllotaxy only gradually passes into the distichous and 

 that the two rows of leaves often exhibit irregularities. First of all the 

 'prophylls' occur right and left on the lateral bud, enveloping it through 

 the concrescence of their edges (Fig. 51). After them follow two leaves 

 evidently serving as protecting organs and consequently falling away as 

 the bud unfolds, and they are placed as on the bud of a radial shoot, 

 that is to say, almost at right angles to the median plane of the two 

 rows of leaves. The figures show how the distichous arrangement is 

 fully or almost reached in the later leaves, and this takes place, not, 

 as might be supposed, and as I formerly believed J , by torsion of the 

 internodes, but by a gradual increase of the divergence of the newly 

 formed leaves. Were it produced by torsion the youngest leaves could 

 not stand nearly opposite one another as is often the case. There is 

 here then an influencing of tJic vegetative point itself, which leads to 



FIG. 51. Vaccinium Myrtillus. Transverse section of two lateral buds in which the distichous arrangement 



appears after the first four leaves. 



a change of the positions of leaves, but this does not take place in all buds 

 alike and is probably brought about by light (see Fig. 50, right). 



In other cases a direct change in the leaf-position in the course of 

 the development of the individual leaves cannot be proved, or at least 

 has not been proved in those which will be mentioned. Before however 

 proceeding to speak of individual examples it is to be noted that two 

 different things have to be considered in lateral shoots. First of all 

 their plagiotropous position, and secondly their generally feebler formation, 

 in consequence of the influence of the chief shoot and of their position 



1 See Goebel, Entwicklungsgeschichte der Pflanzenorgane, p. 145. The direction of the plagiotro- 

 pous shoots in the whortleberry is such that they are nearly horizontal in relation to incident light. 

 At the edge of a wood where the illumination is from one side they are erect with the upper surface 

 turned to the light. I may note here that the converse case of a radial (f) arrangement following 

 upon a distichous (i) one also occurs, for example in Liriodendron tulipifera, in which the leaves in 

 the bud are arranged with a divergence of and on the expanded shoot have a divergence off. See 

 Eichler in Sitzungsb. des Bot. Vereins der Provinz Brandenburg, xxii. 



