50 PROBLEMS OF GENETICS 



obscure and it is equally likely that some multiplication of the 

 growing point is the essential phenomenon. 16 



Stockard's interesting experiments 16 illustrate this question. 

 He showed that by treating the embryos of a fish (Fundulus 

 heteroditus) with a dilute solution of magnesium salts, various 

 cyclopian monstrosities were frequently produced. These have 

 been called cases of fusion of the optic vesicles. I would prefer 

 to regard them as cases of a division suppressed or restricted by 

 the control of the environment. Conversely, the splendid dis- 

 covery of Loeb, that an unfertilised egg will divide and develop 

 parthenogenetically without fertilisation, as a consequence of 

 exposure to various media, may be interpreted as suggesting that 

 the action of those media releases the strains already present 

 in the ovum, though I admit that an interpretation based on the 

 converse hypothesis, that the medium acts as a stimulus, is as 

 yet by no means excluded. 



In these cases we come nearest to the direct causation or 

 the direct inhibition of a division, but the meaning of the 

 evidence is still ambiguous. I incline to compare Loeb's par- 

 thenogenesis with the development (and of course accompany- 

 ing cell-division) of dormant buds on stems which have been 

 cut back. 



It is interesting to note that sometimes as an abnormality, 

 the faculty of division gets out of hand and runs a course ap- 

 parently uncontrolled. A remarkable instance of this condition 

 is seen in Begonia " phyllomaniaca" which breaks out into buds 

 at any point on the stem, petioles, or leaves, each bud having, 

 like other buds, the power of becoming a new plant if removed. 

 We would give much to know the genetic properties of B. phyl- 

 lomaniaca, and in conjunction with Mr. W. O. Backhouse I have 

 for some time been experimenting with this plant. It proved 

 totally sterile. Its own anthers produce no pollen, and all at- 

 tempts to fertilise it with other species failed though the pollen 

 of a great number of forms was tried. 



Recently however we have succeeded in making plants which 



15 Cp. R. H. Compton, New' Phytologist, 191 1, p. 249. 



16 Arch. f. Entwickelungsmech., 1907, XXIII, p. 249. 



