DIMORPHISM. 



333 



Pteris qiiadrimmfa, in which the fronds emerging from 

 an adventitious bud are very different from the ordinary 

 fronds. 



Pig. 178. Portion of a frond of Pteris quadriaurita, with an adventi- 

 tious bud, the form of the constituent foliage of which is very diflferent 

 from that of the parent frond. 



Dimorphism. This term, applied specially to the 

 varied form which the flowers or some of their con- 

 stituent elements assume on the same plant, is an 

 analogous phenomenon to what has been above spoken 

 of as heterophylly, and, like it, it cannot, except under 

 special circumstances, be considered as of teratological 

 importance. A few illustrative cases, however, may 

 here be cited. 



Sir George Mackenzie describes a variety of the 

 potato^ {Solanum tuberosum) ^ which produces first double 

 and sterile flowers, and subsequently single fertile ones ; 

 the other portions of the plant do not differ much. 



' ' Gard. Chron.,' 1845. p. 790. 



