DORSIVENTRAL SHOOTS. POSITION OF ORGANS 



89 



We find it also in many leaves. Whilst we may hold that this position 



is utilitarian because the development of the branches on both sides would 



bring about an overlapping of them which would interfere with their 



function, we cannot yet say anything about the original conditions under 



which it arose. The case of Antithamnion Plumula, represented in Fig. 43, 



is specially striking. Long shoots and short shoots l are seen here ; some 



short shoots stand on that side which is in the plane of the paper, and 



these form the special framework 



of the plant, others occur upon the 



other surfaces both above and 



below. The latter are in much 



smaller number and serve as it 



appears only as a protection to 



the young parts, as they are 



specially found in the positions 



where a lateral long shoot is 



formed. In the long shoots the 



branching is predominant upon 



the outer side and is retarded 



upon the inner side, whilst each 



short shoot produces branches only 



upon the side which is turned to 



the chief axis. Euptilota Harveyi, 



represented in Fig. 46, shows a 



predominance of the branching on 



the outer side of the long shoot 2 . 



Whilst now the immediately 

 inciting causes of these phenomena 

 are unknown, and we can only say 

 of them as of the segmentation of 

 many leaves that they result in 

 one of the many possible construc- 

 tions by which the best use of the 





 IS 



FIG. 46. Euptilota Harveyi. Apex of a long shoot. On 

 if niQiT- eactl se S lnent 'here are two unequally sized short shoots. 

 i, it may Below on the right a long shoot has developed, the lateral 



nnf hf <5imprfliiAll<; rn rpmarl- fViof branches of which are arrested upon the side of it turned 

 HOC DC SUpernUOUS tO remark mat towards the chief axis. After Cramer. 



relationships lie before us here 



which repeat themselves in the same way in the lower and in the 

 higher plants, and that they offer therefore a subject for the most search- 

 ing examination. 



In the following pages the more important forms of dorsiventral 

 construction will be dealt with. It is scarcely possible to group them 



1 See page 35. 



2 See the right lower side of Fig. 46. 



