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Show 286 CONSTITUTIONAL VIGOUR CHAP. VIII. After the crossed or tho self-fertilised plants had once grown decidedly taller than their opponents, a still increasing advantage would tend to follow from the stronger plants robbing the weaker ones of nourishinent and overshadowing thein. This was evidently the case with the crossed plants of Viola tricolor, which ultimatoly quite overwhelmed tho selffertilised. But that the crossed plants have an inherent superiority, independently of co1npetition, was sometimes well shown when both lots were planted separately, not far distant fro1n one another, in good soil in the open ground. This was likewise shown in several cases, even with plants growing in close competition with one another, by one of the self-fertilised plants exceeding for a time its crossed opponent, which had been injured by some accident or was at first sickly, but being ultimat ly conquered by it. 11he plants of the eighth gen ration of I poinooa were raised from small seeds produced by unhealthy parents, and the s If-fertilised plants grew at first very rapidly, so that when the plants f both lots were about three feet in height, the moan height of the crossed to that of the self-fertilis d was as 100 to 122; when they were about six feet high the two lots were very nearly equal, but ultirnately when b tween eight and nine feet in height, the crossed plants asserted their usual superiority, and were to the self-fertilised in bejg-ht as 100 to 85. The constitutional superiority of the crossed oyer the self-fertilised plants was proved in another way in the third generation of Min1ulus, by self-fertilised see:ls being sown on one side of a pot, and after a ce1·tam interval of time cross d seeds on the opposite side. ~rhe self-fertilised seedlings thus had (for I ascertained that the seeds germinated simultaneously) a clear adrvtmtage CHAP. VIH OF 'rHE CROSSED PLANTS. 287 over the crossed in the start for the race. Nevertheless they were easily beaten (as rna y be seen under the head of Mimulns) when the crossed seeds were sown two whole days after the self-fertilised. But when the interval was four days, the two lots were nearly qual throughout life. Even in this latter case the crosse l plants still possessed an inh~rent adv~ntage, for after both lots had grown to theu full height they were cut down, and without being disturbed were transferred to a larger pot, and when in the ensuing year they had again grown to their full height they were Ineasured; and now the tallest crossed plants were to the tallest self-fertilised plants in height as 100 to 75, and in fertility (i.e., by weight of seeds produced by an equal number of capsules fron1 both lots) as 100 to 34. M v usual method of proceeding, namely, to plant seve;al pairs of crossed and self-fertilis~d s~eds in an equal state of germination on the opposite SI~es of the same pots, so that the plants were subJected. to moderately severe mutual competition, was I tlnn~\: the best that could have been followed, and was a fau test of' what occurs in a state of nature. For plants sown by nature generally con1e up crowded, an~ ~re almost always exposed to very severe competitio?with one another and with other kinds of plants. This latter consideration led me to make some trials, chiefiy but not exclusively 'vith Ipomcea and Mimulus, by sowing crossed and self-fertilised seeds on the opposite sides of large pots in which other plants had long been growino· or in the midst of other plants out of doors. b' ~rhe seedlings were thus subjecte~ to v.ery ~evere competition with plants of other k1nds ; and 1n all such cases the crossed seedlings exhibited a great superiorit; in their power of growth over the selffertilised. |