DORSIVENTRAL LATERAL SHOOTS 97 



lateral shoots only. Comparison of a number of allied plants convinces 

 us that the radial position of leaves is the primary, and that the distichous 

 must be considered in many plants as a consequence of the lateral 

 position. When we see in one and the same genus, Betula, the lateral 

 shoots in some species distichously-leaved whilst in others they are 

 radial, and in the genus Corylus observe a progression from Corylus 

 Colurna with its radial orthotropous chief stem to Corylus Avellana 

 in which the distichous plagiotropous shoots predominate, it is evident 

 that the extreme case will be that in which, as I have already said, 

 the radial construction is limited to the primary shoot of the seedling 

 whilst all the others show a marked dorsiventrality. We find this in 

 Corylus, Carpinus, Fagus, Ulmus, and Tilia 1 , in the position both of the 

 leaves and the lateral buds ; the two rows of leaves are not opposite one 

 another but somewhat approximated upon the under side of the shoot-axis ; 

 the insertions of the leaves do not run quite transversely to the long axis 

 of the shoot but slightly obliquely (Fig. 49), so that the upper side of 

 the leaf is directed somewhat obliquely upwards and then a torsion 

 of only some 45 at the base of the leaf-stalk is required in order to 

 bring the surface of the leaf horizontal or parallel with the long axis of the 

 twig. The lateral buds do not however stand in the median plane of 

 the leaf but higher up and approaching its upper stipule, just as they 

 do in so many other dorsiventral shoots. 



The lateral shoots not infrequently assume a leaf-like habit, and 

 when they do so they also conform with leaves in their limited growth, 

 and like leaves have a joint at their insertion upon the chief axis. 

 The special cases of phylloclades will be referred to in the special part 

 of this book and are not noticed here, but as example I shall take 

 the behaviour of some species of Phyllanthus -. In Fig. 53 there is 

 a representation of Phyllanthus mimosoides which shows apparently 

 the bipinnate leaves of many Leguminosae, and from this the specific 

 name has been derived ; the same may be said of Phyllanthus lathyroides 

 and others. We have however here really to do with twigs clad with 

 distichous leaves as the fact of their bearing flowers shows. The chief 

 axis and the stronger lateral shoots produce scale-leaves only arranged 

 in a spiral phyllotaxy, and in their axils the smaller lateral shoots 

 arise. I have proved by experiment 3 that in Phyllanthus lathyroides 

 the distichous shoots may be transformed into radial ones so long as 



1 Hofmeister, Allgem. Morphologic, p. 609, includes Aristolochia Clematitis amongst plants in 

 which vertical axes have a f phyllotaxy whilst the shoots springing from them at an angle have 

 distichous leaves. I do not know the seedling of this plant, but I find on the orthotropous 

 adventitious root-shoots the | position of the leaves_/"ww the beginning. 



2 Dingier, Die Flachsprosse der Phanerogamen, Heft I : Phyllanthus. Miinchen, 1885. 



3 Goebel, Uber Jugendformen von Pflanzen und deren kiinstliche Wiederhervorrufung, in Sitz- 

 ungsber. d. kgl. bayer. Akad. d. Wissensch., xxvi (1896). 



GOEBEL H 



