DEVELOPMENT OF PLANTS 413 



two outer ones are shorter than the others (Fig. 309, C). The 

 ovary is divided into two compartments by a membranous parti- 

 tion. The fruit is generally a capsule that usually opens by two 

 valves, as seen in Fig. 309, F. This large family of over 1,800 

 species is almost universally distributed over the earth and of 

 very common occurrence. They are among the most familiar 

 weeds of waste places, fence rows and barren fields, and this 

 unfavorable situation has perhaps resulted in the reduction in the 

 size of the flowers which are usually small and of a pale-yellow 

 or white color. They have the advantage of being grouped into 

 conspicuous inflorescences, a tendency that will be noted again 

 and again in higher orders. These flowers are of a more special- 

 ized type than in the open blossoms of the buttercups and poppies, 

 and present a variety of interesting devices that can only be 

 hinted at in this lesson. More commonly, perhaps, the stigmas 

 are receptive as soon as the flower opens and the anthers are still 

 closed, thus ensuring crossing. The short stamens are more fre- 

 quently utilized only for crossing since they are below the stigma 

 and so placed as to be in line with the nectar glands that are 

 often located in sac-like enlargements of the perianth. The four 

 long stamens are variously related to the stigmas. Sometimes 

 they are below the stigma and when open are of service only for 

 crossing, but later they elongate and bear some of the spores to 

 the stigma. The reverse position of the sporophylls also occurs, 

 but the outward opening of the anthers keeps the microspores 

 from dropping by chance on the stigma until the stigma is finally 

 lifted up to the anther by the elongation of the style, where it is 

 sure to be dusted with spores, as the anthers open wider and 

 wider. Certain species are characterized by an extraordinary 

 twisting of the filaments, so that for a time the anther is turned 

 away and bent over towards the perianth so as to be in line with 

 the nectar glands, and later, at the close of the flowering period, 

 a reversal of this bending brings the anther in contact with the 

 stigma. These illustrations are sufficient to show that the flowers 

 have many arrangements and exact movements that result in 

 crossing, or, if this fails, in autogamy. It should be stated that 

 several of these plants get along very well without crossing. 



