nr.] EXPERIMENTAL PROOFS 33 



their hereditary character, but instead of their 

 being long and stout, they were not an inch 

 long, and like needles. This proved the spines 

 to be an hereditary feature. In the second 

 year there were none at all ; moreover, the 

 plants blossomed, and, taken altogether, there 

 was no appreciable difference from O. repens, L. 



As an example of experimental cultivation, the 

 late Dr Sickenberger of the School of Medicine, 

 Cairo, raised a plant of Zilla myagroides (fig. 4) 

 in the Botanic Garden. It is common in the 

 Waddys of the desert, being a crucifer about 

 3 feet high, and intensely spiny. Spines were 

 produced in the first year by heredity; but 

 they had already begun to be arrested, for I 

 found the anatomical structure to be far less 

 consolidated, the woody and sclerenchymatous 

 tissues very lax compared with that of the 

 spines in the desert. To judge by their appear- 

 ance they would probably have required more 

 than one year to disappear altogether. 



From these and many other instances, such 

 as wild, spinescent trees, e.g., plum and pear, 

 which lose their spines under cultivation, we 

 may safely generalise ; for a careful search will 

 soon show Nature at work in modifying plants, 

 and changing them from xerophytes to meso- 

 phytes, or vice versa, so that, first, by the 

 accumulation of coincidences or induction ; 

 secondly, by experiments, both artificial and 



