196 Mr. W. Baleson. Heredity, Differentiation, 



poses in- this paper to find a numerical value for the average correla- 

 tion between undifferentiated like parts of the same individual. A 

 large series of heterogeneous cases of various organs in various plants 

 have been investigated. The values found range from -1733 to 

 8607. Eeasons are put forward for excluding some of the highest 

 and for doubting the validity of others, especially some of the lower 

 ones. Eventually the average result -45 is again reached, taken on a 

 series ranging from '1733 to "6311. 



Professor Pearson attaches importance to the rather close similarity 

 between the two average values. We are bound, therefore, to remark 

 as a suspicious circumstance that the range of values is so wide, and 

 that the average value should so nearly approach the mean of the whole 

 possible range ; but upon this point I do not propose to dwell, preferring 

 to deal with more general aspects of the problem. 



Now Professor Pearson is attempting to measure to what extent 

 there is a resemblance or correlation between repeated parts of one 

 individual as compared with the same parts of different individuals of 

 the same race : how much, that is, of the resemblance between repeated 

 parts of an individual is due to its individuality 1 Further, how much 

 on an average of many individuals may be expected to be due to 

 individuality 1 



For various sources of error Professor Pearson is well prepared. In 

 his Malm material, for instance, he finds little correlation due to indi- 

 viduality ; because, as he points out, his specimens may have been all 

 or largely the vegetative product of one or few individuals. In some 

 Mushrooms, on the contrary, he finds this correlation high, but he 

 thinks that here individuality may partly be due to stages of growth, 

 for his individuals were not all of similar age. In comparison with 

 what/ follows these sources of error are trifling. 



It will be remembered that the series of homotypes is to be undif- 

 ferentiated. If differentiation exists and is not recognised the apparent 

 homotyposis due to individuality will, as Professor Pearson perceives^ 

 be immediately lowered. In order, therefore, that the inquiry should 

 have significance, it is necessary that differentiation occurring between 

 members of a series of parts should have a clear meaning as distinct 

 from variation occurring amongst them ; and further, in order that the 

 investigation should be carried through, we must be able to discrimi- 

 nate such differentiation from variation. On critical consideration it 

 will be apparent that neither of these postulates accords with the facts 

 of nature. I cannot find that Professor Pearson has in any real way 

 dealt with this difficulty. The practical difficulty he has perceived and 

 in part met, but the more serious theoretical difficulty has, I think, 

 escaped him. When fully understood, it will surely be seen to 

 invalidate the whole argument. 



Let us grant for the moment that differentiation of the parts can be 



