SUPPLEMENT 119 



mena of regeneration show us also that not only propagative but almost all 

 cells indeed we might say all cells originally bear all initials of the 

 organism ; hence the quite special question arises what are really these initials, 

 and where are they to be looked for ? 



Hitherto we have used the word ' initial ' to signify briefly that the plant 

 possesses a quite definite developmental capacity. We have not suggested, 

 as the word ' initial ' might be thought to indicate, that the character in 

 question was represented in the plant by some structure of microscopic or 

 ultra-microscopic size. For a long time one has felt the necessity of attempt- 

 ing a more accurate determination of the nature of these initials, and recently 

 special hypotheses, based on certain histological evidence, have gained ground. 

 All these hypotheses have this in common, that they postulate a definite part 

 of the cell as the material substratum or seat of heredity. While, to commence 

 with, the nucleus as a whole (HAECKEL, 1866 ; STRASBURGER, 1884 ; DE 

 VRIES, 1889) was invested with this duty, more recently it has become more 

 and more the custom to ascribe the function to a part of it, viz. the chromo- 

 somes,. It is assumed that the chromosomes are permanent organs of the 

 nucleus, multiplying by longitudinal division. In fertilization the same number 

 of chromosomes are contributed by father and mother, and by the fusion of 

 these it is believed that both parents may thus have an equal influence on the 

 form of the resulting offspring. During the entire vegetative life of an organism 

 the chromosomes of its nuclei are always half paternal and half maternal, 

 but only just before the formation of new sexual cells, at the commencement 

 of reduction division, a fusion of homologous chromosomes in pairs takes 

 place, after which longitudinal splitting begins once more. The fusion must 

 permit of an exchange of the very minute bearers of individual initials, and 

 the renewed longitudinal splitting must then furnish the basis for the law of 

 segregation. 



These few remarks must suffice at present, and the reader interested in 

 the subject is referred for further details to STRASBURGER'S monograph (1905 b). 

 It is obvious that we have here to deal with doubtless very ingenious interpreta- 

 tions of the observed facts of karyo kinesis. There are many points, however, 

 in this most recent branch of science which to the physiologist appear open 

 to criticism. In the first place, the observations made in recent years as to 

 the changes going on in the nucleus have led to very diverse conclusions. 

 Although nowadays these have become more harmonized, still it must be 

 remembered that this harmony has arisen under the influence of a hypothesis 

 which has yet to be proved ; it would appear possible that, sooner or later, 

 we shall be provided with explanations of reduction division other than those 

 we are as yet familiar with. In view of the great difficulty of the subject this is 

 only what might be expected. Not only are the actual facts of mitosis not as 

 yet perfectly settled, but their interpretation is uncertain. We are ignorant 

 whether the interchange of characters is exclusively associated with the nucleus, 

 and with the chromosomes more especially ; there are many grounds for 

 believing that the protoplasm also has a share in heredity. Further, there is 

 no experimental evidence available in any part of the subject ; the explana- 

 tions offered take into consideration, in a one-sided manner, certain simple 

 possibilities without excluding others ; hence, in spite of the great interest it 

 has aroused, the subject has not received the attention it deserves in treatises 

 on Physiology. While referring to the special literature on the subject 

 quoted in STRASBURGER'S works (1905 a, 1905 b, 1907), we need only put 

 forward one reason which appears to negative the view that only the nucleus 

 is the bearer of hereditary characters, and we do this because we come to 

 know in this way of new and important facts bearing on the subject. 



It has been stated above that in hybrids, in the long run, in single parts 



