stout: pollinations in cichorium intybus 359 



reported of which thirteen were sterile, and four gave less than 

 fifty per cent of the full fertility. Of the total of more than 500 

 hybrids of the several generations only forty-two were used in 

 intercrossing. While East admits that the evidence indicates the 

 possibility of "true cross-sterility" he is inclined to view the 

 partial or feeble fertility seen in four crosses as accidental. East 

 finds that in the self-pollinations, pollen germinates abundantly, 

 but the tubes show no acceleration of growth when they penetrate 

 nearer to the ovaries as do the pollen tubes in cross-fertilization. 

 This we may note is in accord with numerous observations made 

 by Scott, Miiller, Darwin, Hildebrand, Jost, and Correns. Quite 

 in common with Jost, East considers that the pistils produce 

 stimulating substances, but further assumes that the secretion 

 of such substances is "called forth only by a gamete that differs 

 from the somatic cells between which the pollen tube passes." 



According to this view self-sterility is largely an individual 

 matter depending on too great a similarity or a lack of necessary 

 constitutional differentiation which is in this particular quite the 

 view of Darwin, Jost, and Correns. The conception differs especi- 

 ally from Darwin's in limiting the operating dissimilarity to the 

 pollen grains: the pollen must possess in its constitution at least 

 one hereditary element which is not present in the more complex 

 pistillate cells. No matter how simple or how complex a pistil 

 may be, pollen tubes will grow well, provided they possess some 

 different element. The view differs radically from that of Baur, 

 Correns, and Compton in assuming that there are no specific 

 factors, anlages, or determiners which are directly concerned with 

 fertility or sterility, and which are inherited as such. The in- 

 ference is that the ability to form the specific enzymes and stimu- 

 lating substances is present in all plants of the race or series of 

 hybrids. The production of the necessary enzymes in the pollen 

 tube and their subsequent action in calling forth secretion in the 

 pistil is conditioned by the one-sided dissimilarity as noted above, 

 and is a secondary property of the general hereditary complex. 



The fundamental conception is, of course, that the germ cell 

 constitution is made up in part at least of definite units which 

 are anlages, either directly or in combination with other units, 

 for the expression of characters. This raises the highly important 

 question whether such units exist with anything more than rela- 



