F. J. (hiriTKNDKN 39 



It is this form of fruit which is called parthenocarpic, but it is not 

 yet clear whether pollination of any sort is necessary for the production 

 of these seedless fruits. In cucumbers it certainly is not, for commerci- 

 ally grown cucumbers reach a large size without fertilization of any kind, 

 and contain no fertile seeds. The histories of many seedless fruits, 

 like the banana, and of the well-known seedless oranges, aiul other 

 seedless fruits, seem never to have been thoroughly worked out, though 

 something has been done with seedless grapes by Miiller Thirgau. 

 There may well be two tyjies of parthenocarpy. 



Further, it is not yet clear whether, in the case of the relatively 

 few apples and pears which produce seed without the intervention of 

 foreign pollen, the seed is produced parthenogenetically or not. 



Parthenocarpic fruits are almost nnknown in the plum and cheriy. 



Cmtse of Self-slerility. It is in only the rarest cases that apples or 

 pears have unisexual flowers. Both ovules and pollen in some two 

 hundred varieties of apples, and in the same number of pears, which 

 we have examined, are apparently properly developed. The pollen is 

 capable of germination in every variety, though the per cent, of ger- 

 mination varies greatly in different seasons. So far as our experiments 

 have gone, it seems that the pollen of any variety of apple is capable 

 of fertilizing the egg-cells of any other variety of apples, and similarly 

 with pears. (Backhouse has shown this is not the case in plums and 

 cherries.) Naturally, the enormous number of possible combinations 

 has not yet been exhausted. The point needs further investigation, 

 especially from the economic point of view, for some variety may be 

 better fitted to induce fruit production in some other than are other 

 varieties. There is sufficient evidence, however, to show that, while 

 the pollen of one variety may be quite impotent when apphed to the 

 stigmas of flowers of the same variety, yet it is capable of fertihzing 

 another variety and of inducing the production of viable seed. Extended 

 microscopic examination of the apple flower has failed, so far, to reveal 

 to us, either in its structure or in its development, anything to account 

 for this remarkable state of things, both pollen and ovule appear normal 

 in every way. We have been repaid in the rather time-consuming 

 operations this examination has entailed by the discovery of one or 

 two curious and possibly significant facts hitherto unrecorded, but these 

 facts have no bearing upon the present question. We have, here, a 

 very curious phenomenon, rather wide-spread in the vegetable kingdom, 

 of incompatibility between the gametes of a hermaphrodite flower. 

 Does such incompatibility exist among hermaphrodite animals ? and 



