38 PLANT HYBRIDIZATION BEFORE MENDEL 



(p. 8.) This is the character of the pollen grain and the manner 

 of its germination as Kolreuter conceived it. 



The male fertilizing material, as well as the secretion upon the 

 stigmas, is considered to be of an oily nature. These two secre- 

 tions commingle with one another, when they come together, in 

 the most intimate manner and make, after commingling, a uni- 

 form mass, which, when fertilization ensues, is sucked in by the 

 stigma, and must be conducted through the style to the ovules, — 

 the so-called "seed-eggs" (Saameneyern) or unfertilized "germs" 

 (Keimen). Kolreuter recognizes that a certain number of pollen 

 grains are required for fertilization in every flower, but this 

 number, in comparison with the number produced, is very small. 

 Kolreuter remarks that, in a Ketmia flower of average size, 4,863 

 pollen grains are produced, but that, for the fertilization of the 

 30-odd seeds in a single capsule, not more than 50-60 pollen 

 grains are required. He found that, the more the number of pol- 

 len grains fell below this number, proportionately fewer were the 

 number of seeds produced. If as few as 15 or 20 pollen grains 

 were used, only 10-16 seeds were fertilized, (p. 12.) It was found, 

 moreover, that with this small number of pollen grains the seed 

 capsule after a time began to wilt, and finally fell off. If fewer 

 than 10 pollen grains were used, "then it was just as though 1 

 had taken none at all." No trace of fertilization followed, and 

 the ovary degenerated and fell off, in still less time. This ex- 

 periment tallies closely with the preceding one, in demonstrating 

 that, in the species in question, about two pollen grains are re- 

 quired on the average per ovule, making allowances for the 

 failure of some grains to germinate, and for the failure of the 

 pollen tubes of others to reach the ovary. These latter details 

 were entirely unknown to Kolreuter, who believed he was dealing 

 with a mass effect. In the common Mirabilis jalapa the number 

 of pollen grains reached 293, and in a Peruvian species, 121 ; but 

 of this number but one, or at most two or three, were required 

 for fertilization. Kolreuter found by experiment that in a plant 

 with 2-5 stigmas, by abscission of all but one, and pollinating 

 that one "with a sufficient quantity of pollen" (p. 13), ripe seeds 

 developed in all the cells of the ovary. He states this was found 

 even to be the case in plants in which the stigmas were separated 

 to the base, as in Paris. This was so also in Hypericum he says, 



