TWENTY-FIRST ANNUAL MEETING. 



43 



The function of the pollen is to fertilize the ovules in the pistil, that 

 they may develop and form seeds. It consists of a mass of gelatinous 

 substance known as protoplasm, and is surrounded with two cell walls. 



When fully developed, the walls of the anthers burst and the pollen 

 grains escape. If brought into contact with the stigmatic surface they at 

 once send out pollen tubes (Fig. Ill, h), as they are called, which work 

 their way down through the tissues of the style and penetrate the ovules. 

 The nucleus unites with the nucleus of the ovule, and the act of fertiliza- 

 tion is accomplished. 



Having considered the structure of the flowers, and the functions of the 

 different organs, let us stop for a moment and ascertain how these parts 

 have been formed. By the botanist the four parts that go to make up a 

 complete flower are regarded as merely modified leaves. The sepals are 

 generally green in color and the resemblance can easily be seen. The 

 petals are also leaf like in their structure, but in the stamens and pistils 

 a much closer examination will be required to establish the relationship. 

 It can be shown that in many plants, as in the pea and bean, the pistils are 

 identical in appearance with folded leaves, and in case of the stamens we 

 know that they are transformed into petals, in the case of double flowers 

 and then the resemblance to leaves is quite marked. 



It has been noticed that in some species of plants, the length of the 

 stamens and pistils is not constant in all flowers, as in one we may find 

 long stamens with short pistils (Figs. V. VI), and in another plant of the 

 same species there may be short v 



stamens and long pistils. 



Charles Darwin spent months in 

 studying this peculiarity, and has 

 given the results to the public in his 

 book, "Different Forms of Flowers 

 in Plants of the Same Species." 

 He found, as the almost invariable 

 result of hundreds of experiments, 

 that far better results were obtained 

 when pollen from the long stamens 

 was placed on long pistils, than 

 when they were allowed to fertilize 

 the short pistils. As the short pistils were in the same flowers with the 

 long stamens, this was of course self-fertilization, and the results were 

 identical with those also published by Darwin in " Cross and Self Ferti- 

 lization in Plants," and he explains the diversity in the length of the 

 essential organs as one of the means employed by nature to bring about 

 cross-fertilization. 



In the flowers where these differences were noted, the aid of insects in 

 transferring the pollen is necessary, and the different lengths rendered it 

 more likely that a cross would be secured. It was also found that, if pol- 

 len from the anthers of one plant was applied to the pistil of another, on 

 the same plant, far better results were obtained than when it was applied 

 to the pistil of the same flower; and if the pistil belonged to a flower of 

 another plant, the results would be even more favorable, and a very marked 

 increase in the amount of seed produced would be obtained. 



In order to secure the benefits of cross-fertilization to plants, it is nec- 

 essary to invite the presence of insect visitors. One of the means that nature 

 has cjevised is the bright and showy colors of calyx and corolla. White 





