KNOWLEDGE OE THE MUTATING- OENOTHEEAS. 



35 



characters, in cultures of 75 races related to O. grandijlora, so that evidently tlie 

 dwarfing of O. nanella is not primarily due to a parasite, although the presence of hacteria 

 may make it smaller than it otherwise would be. 



In the case of O. gigas, I have shown (1909 d) that the larger size of the plant 

 is fundamentally concerned wath the larger size of the cells and their nuclei, which in 

 turn is connected in a causal relation with the doubled number of chromosomes. Pre- 

 liminary measurements of cell-size ia 0. nanella, by a student, indicate that they are 



considerably smaller than the 



espondin 



in O. Lamarckicma 



I 



pect 



investigate the question of cell-size in O. nanella more fully, but in the meantime it is 

 very probable that the small stature of O. nanella may be at least partially explained on 

 the basis of the cell-size, the dwarfness being a character of the cell. The many other 

 changes in the shape of leaves, etc., are probably, like those of 0. gigas, not so simply 



plained (cf. Gates, 1909 d, 1911 



It seems evident, in any case, that the dwarfness 



of O. nanella is a cell problem (although the number of chromosomes remains 14) and 

 is not produced by any pathological condition induced by other organisms. 



Gaucliery (1899) (and other papers might be cited) classes dwarfing as of two kinds, 



titutional nanism, (2) induced nanism. From 



anatomical examination of 



number of dwarfs, he concludes that the reduction in the number of elements in the stem, 

 and in their calibre, is very variable according to the tissue considered. Thus, the dimen- 

 sions of the xylem vessels are always reduced, but this is not always true of the 

 dimensions of the other cells ; and in one case there is even shown an increase in the 

 size of the cortical cells, though in all the other elements of the stem there is a decrease 

 in size. The reduction in the dimensions of the epidermal cells was found to be much 

 less than in the vessels. 



O. lata and O. semilata. 



The mutant 0. lata has occurred a number of times in my cultures, as shown in the 

 following table : — 



Table III. 



Culture. 



Number 



of 

 plants. 



0. ruhrinervis 



0. Lamarckiana x 0. hrevistylis 



9t5 



Number 



of 



0. lata. 





1 



0. Lamarckiana 



0. ruhrinervis X 0. nanella 



92 



117 



3 



2 



0. ruhrinervis x 0. Lamarckiana 

 (from 0. lata x 0. Lamarckiana). 



42 



64 



1 



1 



Total 



411 



8 



1'95 per cent. 



PL 3. fig. 42 shows a typical rosette. 



The very characteristic buds are sho\>n in 



p2 



