70 



all of different size. If one imagines further that subsequently, when 

 the stem develops, one leaf arises in each area, then it will be clear 

 that successive leaves will be placed with respect to each other at 

 angles of divergence of 13730'28". This will be the divergence too, 

 when the stem has grown out into a cylinder. 



The reason why the meristematic substance should often be distri- 

 buted as described above, but in other cases (for instance in decussate 

 phyllotaxis) follows a quite different pattern, has not been made clear 

 to my mind by BEIJERINCK. Neither did he explain how the "contact 

 spirals" are produced which one may draw through the leaves at the 

 growing-point, these spirals being usually of another type and 

 present in other numbers than the contact spirals of BEIJERINCK'S 

 construction. 



BEIJERINCK does describe original experiments from which it 

 appears that there sometimes occur stresses in a layer of drying col- 

 loidal matter which may lead to orthogonal cracks, resulting in a 

 division of the layer into square areas, but the preference of special 

 "angles of inclination" of the borderlines of the areas in the meristem- 

 atic cell-substance, which forms the basis of his theory, could not be 

 made plausible by these experiments. 



The significance which BEIJERINCK attached to this study and the 

 fact that it took the greater part of his time during the last years of 

 his life may justify my having tried to give an elucidation of this work, 

 which in spite of its shortcomings may certainly be called original 

 and remarkable. 



