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128 



GOOD FROM CROSSING. 



Chap. XVII. 



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reversed case. The self-fertilised and crossed seeds thus obtained were 

 allowed to germinate in the same glass vessel on damp sand ; and as the 

 seeds successively germinated, they were planted in pairs on opposite 

 sides of the same pot, with a superficial partition between them, and were 

 placed so as to be equally exposed to the light. In other cases the self- 

 fertilised and crossed seeds were simply sown on opposite sides of the 

 same small pot. I have, in short, followed different plans, but in every 

 case have taken all the precautions which I could think of, so that the 

 two lots should be equally favoured. Now, I have carefully observed 

 the growth of plants raised from crossed and self-fertilised seed, from 

 their germination to maturity, in species of the following genera, namely 

 Brassica, Lathyrus, Lupinus, Lobelia, Lactuca, Dianthus, Myosotis Pe- 

 tunia, Linaria, Calceolaria, Mimulus, and Ipomcea, and the difference in 

 their powers of growth, and of withstanding in certain cases unfavourable 

 conditions, was most manifest and strongly marked. It is of importance 

 that the two lots of seed should be sown or planted on opposite sides of 

 the same pot, so that the seedlings may struggle against each other ; for if 

 sown separately in ample and good soil, there is often but little difference 

 in their growth. 



I will briefly describe the two most striking cases as yet observed by 

 me. Six crossed and six self-fertilised seeds of Ipomcea purpurea, from 

 plants treated in the manner above described, were planted as soon as they 

 had germinated, in pairs on opposite sides of two pots, and rods of equal 

 thickness were given them to twine up. Five of the crossed plants _ 

 from the first more quickly than the opposed self-fertilised plants f the 

 sixth, however, was weakly and was for a time beaten, but at last its 

 sounder constitution prevailed and it shot ahead of its antagonist. As 

 soon as each crossed plant reached the top of its seven-foot rod its fellow 

 was measured, and the result was that, when the crossed plants were seven 

 feet high, the self-fertilised had attained the average height of only five 

 feet four and a half inches. The crossed plants flowered a little before, 

 and more profusely than the self-fertilised plants. On opposite sides of 

 another small pot a large number of crossed and self-fertilised seeds were 

 sown, so that they had to struggle for bare existence ; a single rod was 

 given to each lot: here again the crossed plants showed from the first 

 their advantage ; they never quite reached the summit of the seven-foot 

 rod, but relatively to the self-fertilised plants their average height was as 

 seven feet to five feet two inches. The experiment was repeated in the 

 two following generations with plants raised from the self-fertilised and 

 crossed plants, treated in exactly the same manner, and with nearly the 

 same result. In the second generation, the crossed plants, which were 

 again crossed, produced 121 seed-capsules, whilst the self-fertilised plants, 

 again self-fertilised, produced only 84 capsules. 



Some flowers of the Mimulus luteus were fertilised with their 

 pollen, and others were crossed with pollen from distinct plants growing 

 in the same pot. The seeds after germinating were thickly planted 

 on opposite sides of a pot. The seedlings were at first equal in height ; 

 but when the young crossed plants were exactly half an inch, the self- 



own 







