532 ANGIOSPERMAE—MONOCOTYLEDONES 



von Liebenberg as rendering the action of foreign pollen effective is, in Rimpau's 

 opinion, not general ; he considers that self-pollination takes place even if few fruits 

 are set. 



Beijerinck also describes the rye as self-sterile. 



Rimpau (Landw. Ztg., Wien, xxx, 1880, p. 333) states that fertilization is certain 

 and effective in proportion as the pollinated flower and the pollen with which it is 

 dusted are of dissimilar origen. 



Kirchner (' Flora V. Stuttgart," p. 158) describes the flower mechanism of the 

 species as follows. The flowers are homogamous, but the anthers do not dehisce 

 until they project from the widely divergent glumes and have bent downwards. The 

 stigmas protrude between the glumes, and remain outside for some time after they 

 have closed again. Cross-pollination is thus usually effected, autogamy only rarely 

 taking place with self-sterility as a result. In favourable weather the flowers begin to 

 open after sunrise, and anthesis lasts until evening. The first flowers to open are 

 situated at a height of two-thirds of the length of the spike ; each remains open for 

 a quarter of an hour. In unfavourable weather the flowers do not open, and 

 fertilization is excluded. 



1016. Elymus L. 



3067. E. sabulosus Bieb. — The flowers of this species are homogamous, but 

 Hildebrand says that the receptive stigmas project from the flower for some time 

 after the closing of the glumes. 



1017. Hordeum L. 



3068. H. vulgare L. — Delpino states that in this species the flowers of the two 

 middle rows never open, but fertilize themselves cleistogamously, while those of the 

 four outer rows are homogamous, with a course of anthesis resembling that of wheat, 

 so that the possibility of cross-pollination is not excluded. Darwin (' Diff. Forms of 

 Fls.') says that species of this genus also possess cleistogamous flowers. 



Von Liebenberg states that the flowers are alreadly self-pollinated before the 

 spike protrudes from the leaf-sheath. 



Godron asserts that the flowers of all six rows open. 



Kerner states that the pollen is scattered between 5 and 6 a.m. According to 

 Rimpau the flowers open at a temperature of 12^° C. He says that the middle 

 spikelet seems to fade almost always with closed glumes, the latter only diverging 

 extremely rarely. The lateral spikelets, however, open regularly. The possibility 

 of cross-pollination is therefore slight. 



3069. H. distichon L. — Delpino states that in this species only the flowers 

 of the two middle rows are hermaphrodite, those of the four others being male, or, 

 according to Hildebrand, neuter. Delpino says that the hermaphrodite flowers 

 usually remain closed, pseudo-cleistogamy then taking place. Sometimes single 

 larger ones open a little, however, so that cross-pollination by the male flowers 

 becomes possible. 



Godron says that the hermaphrodite flowers of the two middle rows only open 

 if the temperature between 8 and 10 a.m. is favourable {18-20° C). 



Rimpau found that either the flowers all open together and their anthers project, 



