62 Heterostylism in Oxalis 



Procedure and Possible Sources of Error. 



As has been already stated, the flowers were not castrated before 

 use, except in the year 1907. The danger incurred can be gathered 

 from the following facts. 



During the five summers of 1907, 1908, 1909, 1911 and 1912 the 

 total number of capsules setting on covered but untouched flowers 

 amounted to 14, of which none were on Long-styled plants, eleven 

 on Mid-styled plants, and three on Short-styled plants. Such capsules 

 may either arise through some insect introducing foreign pollen or 

 from a true spontaneous self-fertilization. Also, aphis were present on 

 some of the plants. But these insects would probably act as self- and 

 not as cross-fertilizing agents, owing to their stationary habits. 



It seems probable that these fourteen capsules did not arise from 

 any outside pollen having reached the stigmas, from the fact that they 

 were all formed on Mid- and Short-styled plants. The protruding 

 Long-styles would be most subject to the contact of any intruder, but 

 no capsules have arisen on untouched Long-styled plants. 



As will be seen from the details in Table VIII these capsules set 

 very few seed, and less than half of these germinated. Also it must 

 be remembered that these fourteen capsules occurred amongst many 

 hundreds of flowers which opened each year under cover but were 

 not used. 



TABLE VIIL 



Capsules setting seed si)ontaneously. 



Giving 



To return to the rare appearance of the third form amongst the 

 offspring of a fertile Long x Mid and Long x Short cross. The 

 question arises : Can these be accounted for by the introduction of 

 a few of the mother's pollen grains ? Where a Long-styled plant is 

 mother, this is clearly not the case, as self-fertilized Longs give Longs 

 only. (See also Lythrum, below.) But three Mids have appeared in 



1 The Mid-plant of 1907 was an ancestor of all the subsequent individuals setting 

 spontaneous seed. There may be self-setting strains. See also Table VII. 



