October 2, 1896.] 



SCIENCE. 



49^ 



liar condition of the limbs exhibiting the 

 phenomenon the diflSculty is not altogether 

 passed, as we must still explain how it hap- 

 pens that all the flowers, which open quite ir- 

 regularly, were pollinated with pollen from the 

 same variety. Mr. Lennox himself calls 

 attention to the difficulty in understanding why 

 such results, if rightly due to the effect of pol- 

 len, as supposed, are not more common con- 

 sidering that cross pollination unquestionably 

 occurs commonly in all orchards, 



I am not familiar with the history of the 

 varieties concerned and cannot suggest whether 

 or not it is possible to consider this a reversion 

 such as sometimes occurs late in the life of an 

 individual. Partial reversion by segments in 

 the same fruit, on certain limbs or the entire 

 tree, is not of uncommon occurrence.* Such 

 stripes, further more, are evidently not neces- 

 sarily due to reversion to characters derived from 

 a cross, but frequently to characters lost by vari- 

 ation. It would seem to me not at all improb- 

 able, from the facts given, that this might be 

 such a case of reversion in certain branches. 

 It should be remembered in this connection 

 that Darwin has given several cases of stripes 

 on apples similar to the case in question, which 

 cannot be explained as effects of cross pollina- 

 tion, f It is a common occurrence for oranges 

 to produce segments of rind resembling lemon 

 or citron, and these are commonly considered 

 to be due to the immediate effect of pollination. 

 These modified segments, however, are not in- 

 frequently found at considerable distances from 

 lemon or citron trees, and they do not occur 

 more frequently, so far as I have been able to 

 observe, when branches of the orange and 

 lemon are near together or interlocked. It is 

 very probable that they are in most cases to be 

 attributed to reversion. Occasionally navel fruits 

 occur on almost all orange and lemon varieties 

 and are commonly believed to be positive evi- 

 dence of the immediate influence of navel pollen. 

 Yet I have proven by numerous dissections that 

 the navel is invariably formed early in the de- 

 velopment of the pistil, weeks before it reaches 

 the stage for pollination. It is well known that 



* See Darwin, Animals and Plants under Domes- 

 tication, II., p. 10. et. seq. 

 tl. c, I., p. 425. 



certain varieties not navels more commonly 

 produce navels than certain other varieties. On 

 these varieties, again, the navel development 

 may be found in some of the pistils long before 

 pollination. The development of the navel is 

 a profound morphological change originating^ 

 early in the development of the pistil, and I 

 think its production lies entirely outside the 

 possibilities of pollen modification. Again: the 

 absence of mature pollen in every navel anther 

 examined by Prof. Van Deman and his assist- 

 ants and myself makes it highly improbable 

 that navel marks in oranges can ever be inter- 

 preted as due to the immediate effect of navel 

 pollen. There is, unquestionably, a marked 

 tendency among the various varieties of citrous 

 fruits to sport in this way, and the isolated 

 cases of navels on other varieties are merely 

 illustrations of this tendency. 



It is not impossible that a combination of the 

 characters of two varieties on a portion of 

 one tree, where two trees of the varieties con- 

 cerned are growing quite near together as in 

 the case described by Mr. Lennox, might be 

 caused by graft hybridization produced by the 

 fusion of roots from the different trees. I am 

 not aware that any such case has ever been re- 

 corded or even suggested, but it is surely within 

 the limits of possibility, as roots from different 

 trees, which become closely associated or 

 crowded together, sometimes fuse. I have ob- 

 served in one case a fusion of two orange roots 

 from different trees and have not infrequently 

 observed the fusion of roots from the same 

 tree. It is probable, however, that the case 

 described by Mr. Lennox could not thus be 

 explained, as I suppose the trees concerned 

 were grafted on other roots. I presume Mr. 

 Lennox is sure that the stock, on which the 

 Greening is grafted, is in no way related to the 

 Talman Sweet or any similar variety, and has 

 never been 'double-worked,' that is, grafted 

 twice with possibly a section of Talman Sweet 

 remaining in the trunk. These are suggested 

 as details which one must know positively before 

 excluding their possible action. 



The immediate effect of pollen is a much dis- 

 puted question in horticulture, and one which 

 demands the most careful experimental evi- 

 dence to satisfactorily confirm. That there is 



