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THE AMERICAN NATURALIST [Vol. XLII 



support of this position the case of Dimorphotheca pluvialis, sl 

 "trimonoecious" form where flowers of three kinds, male, female 

 and hermaphrodite, occur in the same head. Since we have 

 here two kinds of sperm-cells (pollen), one from the hermaph- 

 rodite flower and one from the male flower, and also two kinds 

 of eggs, embryos can arise in four different ways. If the germ- 

 cells had different sex-tendencies after they are built into a 

 male, a hermaphrodite, or a female flower, four kinds of offspring 

 would arise. All the seed, however, produce the same kind of 

 offspring, i. e., trimonoecious forms. Therefore all the germ- 

 cells of Dimorphotheca must bear the tendency again to give 

 origin to trimonoecious plants. It may be said then, that all 

 germ-cells of a hermaphrodite plant have the tendency again 

 to develop into hermaphrodite plants, whether they be found in 

 stamens or pistils. All germ-cells of monoecious forms have the 

 tendency again to produce monoecious forms whether they arise 

 in male or female flowers. We know, then, the tendency of the 

 germ-cells in hermaphrodite and monoecious types and we can 

 employ these known quantities to ascertain by cross-breeding the 

 unknown tendency of the germ-cells of unisexual plants. 



In the first three experiments Dr. Correns employed two 

 species of Bryonia, a genus of the Cucurbitaceae, growing wild in 

 central Europe. Bryonia alba bears a black fruit and is 

 monoecious. Bryonia dioica bears a red fruit and is dioecious. 

 In the first experiment (A) he pollinated the pistils (egg-cells) 

 of Bryonia dioica with the pollen of Bryonia alba. He obtained 

 eleven hybrid offspring from the seed, all female plants and 

 perfectly sterile. These results disclose the following facts: 

 (1) That monoeciousness was here recessive to the dioecious 

 conditions; (2) that the egg-cells of B. dioica had before fertil- 

 ization, "progame," a fixed sex-tendency, and all of the same 

 kind. Were this not the case, not all the offspring could have 

 attained the same sex. Had both anlagen, those of the male 

 and those of the female sex, been equally active in the eggs and 

 had a decision as to the definitive sex depended upon a struggle 

 between the anlagen (or upon external influences), the hybrid 

 offspring would have been of dissimilar sexes; (3) the egg-cell 

 has the tendency to develop into a female plant ; also the tend- 

 ency to give origin to such plants as those from which it arose ; 

 the physiological sex-determination and the developmental tend- 



