DIFFERENTIATION IN FLOWERS. 



not fail to bloom freely as soon as the 

 lengthening days encourage growth, 

 but it is a mistake to force it into flower 

 prematurely by undue heat. Like the 

 Browallia, it requires light sandy soil, 



167 



and strikes root with perfect ease. A 

 variety floribunda is sold, but it is im- 

 possible to imagine anything freer than 

 the type when well grown. 



J. H. B. 



IS DIFFERENTIATION, OR DIFFERENCE IN CONSTITUTION, IN 

 FLOWERS NECESSARY FOR THEIR COMPLETE FERTILITY ? 



(Continued from page 138.) 



The same may be said of the next most I seemingly for the plant's benefit, which in 

 extensive order of flowering plants, the Legu- j reality, were sham arrangements to be set aside 



by a superior effect from cross-fertilization. 



In order to establish Darwin's theory in 

 respect to the beneficial influence of differen- 



The 

 Pea-flowers. 



minosce. "These," Bentham 

 says, "form, after the Compo- 



sites, the most extensive of 

 all the natural orders of flowering plants " 

 (" English Flora," p. 155). In all the flowers 

 of this order the pollen is ripe and shed at a 

 very early stage, when the flowers themselves 

 are but half-grown. When the pollen is shed 

 it falls into the keel and is there, in most cases, 

 stored. This ripening of the pollen takes place 

 in all the flowers before the vexillum is reflec- 

 ted ; before that is reflected, no nectar-seeking 

 insects can gain access to, or come in contact 

 with, either the stamens or the pistils. The 

 flowers are, consequently, peculiarly framed 

 for self-fertilization. The pollen and stigmas of 

 such flowers must have a similar constitution, 

 as there is nothing to intervene whilst they 

 are growing to cause their " differentiation." 

 Their productiveness is evidenced by their 

 universal distribution. Mr. Wallace says, " An 

 immense variety of plants are habitually self- 

 fertilized, and their numbers probably exceed 

 those which are habitually cross-fertilized by 

 insects ("Darwinism," p. 321). Again he 

 says, "It is usually the species which have the 

 smallest and least conspicuous flowers which 

 have spread widely." 



If Darwin's idea that the want of diffe- 

 rentiation between the stamens and pistils of 

 the same flower led to inferiority in fertiliza- 

 tion, then the " great principle "—which he 

 advances when he thinks it supports a theory 

 of his own — " of Nature not lying " (" More 

 Letters of Darwin," vol. ii., 252, 253) would 

 be egregiously violated in the majority of 

 flowering plants. Arrangements would exist 



Mutual 

 Invlgoratlon. 



tiation it is necessary to show 

 that two sets of flowers of the 

 same species which are equally 

 healthy and vigorous, yet grown under diffe- 

 rent conditions, by being intercrossed with 

 each other, mutually affect each other benefici- 

 ally , so that their offspring is thereby mutually 

 itivigorated. If such mutual beneficial result 

 does not follow, but only one set is beneficially 

 affected, it merely shows that one set is in a 

 healthier and more vigorous condition than 

 the other. Darwin gives us the result of one 

 such reciprocal crossing from Knight. " By 

 crossing reciprocally the tallest and the shortest 

 peas," Knight says, " I had in this experiment 

 a striking instance of the stimulative effects 

 of crossing the buds ; for the smallest variety 

 whose height rarely exceeded 2 feet was in- 

 creased to 6 feet ; whilst the height of the 

 large and luxuriant kind was very little dimi- 

 nished ("Animals and Plants," vol. ii., 110). 

 The result, consequently, was both beneficial 

 and injurious, not mutually beneficial. The 

 benefit was limited to the weaker case, and 

 was actually, in its measure, prejudicial to the 

 other. Until " mutual invigoration " is proved 

 we may well suppose, from this case cited from 

 Knight, that bees and insects generally may, 

 by effecting cross-fertilization in different 

 flowers, act both beneficially and prejudicially 

 by their visits. The weaker flowers would be 

 improved by theirfertilization by thestronger; 

 the stronger injured by being crossed with 

 pollen from the weaker. 



