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Show 232 . CANNA WARSCEWICZI. CHAP. VI. not heavier, on the contrary a little lighter, than those from the self-fertilised flowers, as was thrice ascertained. On one occasion I weighed 200 of the crossed and 106 of the self-fertilised seeds and the relative weight of an equal number was as 100 forth~ crossed to 101· 5 for the self-fertilised. With other plants, when the seeds from the self-fertilised flowers were heavier than those from the crossed flowers, this ar peared to be due generally to fewer having been produced by the self-fertiUsecl flowers, and to their having been in consequence better nourished. But in the present instance the seeds from the eros. ed capsules were separated into two lots,-namely, tho. e from the capsules containing over fourteen seeds, and those from capsules containing under fourteen seed. , and the seeds from the more productive capsules were the hea-vier of the two; so that the above explana~ tion here fails. As pollen is deposited at a very early age on tho pistil, generally in contact with the stigma, some flowers \vhilst stm in bud were castrated for my first experiment, and were afterwards fertilised with pollen from a distinct plant. Other flowers were fertilised with their own pollen. From tho seeds thus obtained, I succeeded in rearing only three pairs of plants of equal age. The three crossed plants averaged 32 · 79 inches, and the three self-fertilised ::32 · 08 inches in height; so that they were nearly equal, the crossed having a slight advantage. As the same result followed in all three generations, it would be superfluous to give the heights of all the plants, and I will give only tho averages. In order to raise crossed and self-fertilised p1nnts of the second generation, some flowers on the above crossed plants were crossed within twenty-four hours after they had oxpandecl with pollen from a distinct plant; and this interval would probably not l3e too , great to allow of cross-fertilisation being effectual. Some flowers on the self-fertilised plants of the last generation were also selffertilised. From these two lots of seed , ten crossed and twelve self-fertilised plants of equal ages were rai ed; and these were measured when fully grown. The cro sed averaged 3G · 98, and the self-fertilised averaged 37 · 42 inches in hdght; so that here again the two lots were nearly equal; but the self-fertilised had a slight advantage. In order to raise plants of the third generation, a better plan was followed, and flowers on the crossed plants of the second generation were selected in which the stamens were too short to CHAP. VI. ZEA MAYS. 233 reach the stigmas, so that they could not possibly have been self-fertilised. These flowers were crossed with pollen from a distinct plant. Flowers on the self-fertilised plants of the second generation were again self-fertilised. From the two lots of seeds thus obtained, twenty-one crossed and nineteen self-fertilised plants of equa,l age, and forming the third generation, were raised in fourteen large pots. They were measured when fully grown, and by an odd chance tho average height of the two lots was exactly the same, namely, 35 · 96 inches; so that neither ~:;ide had the least advantage over the other. To test this result, all the plants on both sides in ten out of the above fourteen pots were cut down after they had flowered, and in the ensuing year the stems wore again measured; and now the crossed plants exceeded by a little (viz., 1 · 7 inches) the self-fertilised. They were again cut down, and on their flowering for the third time, the self-fertilised plants had a slight advantage (viz., 1· 54 inches) over the crossed. Hence the result arrived at with these plants during the previous trials was confirmed, namely, that neither lot had any decided advantage over the other. It may, however, be worth mentioning that the self-fertilised plants showed some tendency to flower before the crossed plants: this occurred with all three pairs of the first generation; and with the cut down plants of the third generation, a self-fertilised plant flowered first in nine out of the twelve pots, whilst in the remaining three pots a crossed plant flowered first. If we consider all the plants of the three generations taken together, the thirty-four crossed plants average 35 · 98, and the thirty-four self-fertilised plants 36 · 39 inches in height; or as 100 to 101. We may therefore conclude that the two lots possessed equal 'powers of growth; and this I believe to be the result of long-continued self-fertilisation, together with exposure to similar conditions in each generation, so that all the individuals had acquired a closely similar constitution. XXX. GRAMINAOEJE.-ZEA MAYS. This plant is moncecious, and was selected for trial on this account, no other such plant having been experimented on.* It is * Hildebrand remarks that this species seems at first sio·ht adapted to be fertilised by pollen from the same plant, owing to the ma]e flowers standing above the female flowers; but pmctically it must generally be fertilised by pollen ti·om another plant, a1:1 the |