293 



features in its leaf-anatomy which characterizes the 

 whole group of species; this complex ditlers in the 

 different sections las regards its more minute details, 

 see above). 



(2) The species cannot, without a certain amount of 

 arbitrariness, all be characterized in common. They 

 show differing degrees of protection agaiust exces- 

 sive transpiration, from the highly protected species 

 (S. oppositifolia , Aizoon, Cotyledon, triciispidata] 

 to the very shghtly protected (e. g. the sections 

 Nephrophyllum and Boraphila), in exact correspon- 

 dence with the external conditions of their habitats. 



(3) In the few cases in which we know the same spe- 

 cies, as regards its leaf-anatomy, both from the 

 Alpine regions of Central Europe and from Arctic 

 regions, the specimens from the Arctic regions show 

 less protection against excessive transpiration than 

 the Alpine (for instance they have not their stomata 

 hidden in "calm" interfoliar spaces, free from air- 

 currents, as Lazmewski found to be the case in Al- 

 pine rosette-plants. 



(4) Whether there are any differences between the Arc- 

 tic and the Alpine specimens (besides those per- 

 taining to transpiration) is as yet not known with 

 any certainty, in this paper Arctic specimens, only, 

 having been investigated; Alpine specimens have, it 

 is true, also been investigated, but generally they 

 have been described (and figured) so unsatisfactorily 

 that a comparison would not be entirely reliable. — 

 From the little we know (best from Bonnier and 

 Lazniewski) it appears, however, that in the Arctic 

 leaf there is generally a less decided difference 

 between the spongy parenchyma and the palisade- 

 tissue than in the Alpine, and that the former is 



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