FERTILIZATION IN THE VEGETABLE KINGDOM. 219 



in composition. " The plants on the two sides were always 

 watered at the same time and as equally as possible, and even 

 if this had not been done the water would have spread almost 

 equally to both sides, as the pots were not large. The crossed 

 and self-fertilized plants were separated by a superficial par- 

 tition, which was always kept directed towards the chief 

 source of light, so that the plants on both sides were equally 

 illuminated." Five pairs were thus planted in two pots, and 

 all the remaining seeds, whether or not in a state of germina- 

 tion, were planted on the opposite sides of a third pot, so that 

 the plants were crowded and exposed to a very severe compe- 

 tition. Rods of equal diameter were given to all the plants 

 to twine up, and as soon as one of each pair had reached the 

 summit, both were measured. But a single rod was furnished 

 to each side of the crowded pot, and only the tallest plant on 

 each side was measured. This was followed up for ten gen- 

 erations ; the close-fertilization being always self-fertilization, 

 i. e., by pollen to stigma of the same flower ; the crossing, 

 between individuals in successive generations of this same 

 stock, except in special instances, when an extraneous stock 

 was used as one parent, — to eminent advantage, as will be 

 seen. 



The difference in vigor between the cross-bred and the 

 close-bred progeny, as measured by early growth, was well 

 marked throughout. In the mean of the ten generations it 

 was as 100 to 77. In the tenth generation it was 100 to 54, 

 that is, five cross-bred plants grew to the average height of 

 93.7 inches while the close-bred were reaching the average 

 of 50.4 inches. This was a notably greater difference than 

 in any previous generation. But this was probably accidental 

 or anomalous, for it was not led up to by successive steps. 

 Indeed, the difference in the first generation was a trifle 

 greater than the average of all ten, being as 100 to 76. The 

 second generation was as 100 to 79 ; the third as 100 to 68 ; 

 the fourth as 100 to 86 ; the fifth as 100 to 75 ; the sixth as 

 100 to 72 ; the seventh as 100 to 81 ; the eighth as 100 to 

 85 ; the ninth as 100 to 79 ; the tenth as already stated, 100 

 to 54. The general result is made striking in the following 

 illustration. 



