CRUCIFERAE 113 



pollination. Warnstorf describes the pollen-grains as pale yellow, ovoid or ellipsoidal, 

 very finely papillated, about 37-5 ix. in length and 27-5 /i in breadth. 

 Visitors. — On cultivated plants at Kiel I only observed Meligethes. 



83. Subularia L. 



Minute, homogamous, often cleistogamous flowers. I could not see any nectaries. 



276. S. aquatica. (Axell, 'Om Anord. for Fanerog. Vast. Befrukt.'; Knuth, 

 ' Bl. u. Insekt. a. d. nordfr. Ins.,' p. 30 ; Hiltner, ' Untersuch. ii. d. Gatt. Subularia ' ; 

 Hildebrand, ' Die Geschlechtsvert. b. d. Pfl.') — This plant, which flowers under the 

 water, is cleistogamous. In the land variety I investigated the pollen-covered anthers 

 were very close to the stigma. Hiltner says that in the submerged — and consequently 

 cleistogamous — flowers there are large stigmatic papillae, which receive the pollen 

 directly. More seeds are set than in the chasmogamous variety living on river-banks. 



Visitors. — In Dumfriesshire a fly was recorded (Scott- Elliott, 'Flora of Dumfries- 

 shire,' p. 17). 



84. Thlaspi Dill. 



White or lilac, homogamous and protogynous flowers, with half-concealed 

 nectar. Four nectaries. 



277. T. arvense L. (Herm. Miiller, 'Weit. Beob.,' II, pp. 198-9; MacLeod, 

 Bot. Jaarb. Dodonaea, Ghent, vi, 1894, p. 211 ; Kerner, 'Nat. Hist. PL,' Eng. Ed. i, 

 II, p. 335; Warnstorf, Verb. bot. Ver., Berlin, xxxviii, 1896; Knuth, ' Bl. u. Insekt. 

 a. d. nordfr. Ins.,' p. 30.) — The small white flowers have a green fleshy nectary on 

 either side the base of each short stamen. The anthers of the four long stamens are 

 at the same level or a little higher than the stigma, which matures simultaneously. 

 They turn their pollen-covered surfaces towards the stigma, and are so near it that 

 automatic self-pollination is inevitable. The anthers of the two short stamens are 

 somewhat lower than the stigma, to which they also turn their dehisced sides. They 

 are further from the stigma, and serve for cross-pollination by insect agency. 



Warnstorf says that all the stamens project beyond the stigma, and that their 

 introrsely dehiscing anthers are inclined over it, making autogamy inevitable. The 

 pollen-grains are yellowish-white, ellipsoidal, tuberculated, about 25-30 jx long and 

 20-23 fj. broad. 



According to Kerner there is slight protogyny, but automatic self-pollination 

 takes place later by contact of the anthers with the stigma.— Hieronymus observed 

 cleistogamous flowers. 



Visitors. — Hermann Miiller observed the following in Westphalia. — A. Diptera. 

 Muscidae: i. Anthomyia sp. $; 2. PoUenia rudis Z'. B. Hymenoptera. Apidae: 

 3. Andrena parvula K. %, skg. and po-cltg. ; 4. Apis mellifica L. 5, skg. 



278. T. perfoliatum L. (Kirchner, ' Flora v. Stuttgart,' p. 307.) — The flowers 

 are even smaller than those of the last species, and therefore more inconspicuous ; 

 especially as the petals bend outwards but little. The conspicuousness of the 

 inflorescence is, however, enhanced by the fact that the petals do not fall off" as soon 

 as fertilization is eff^ected. The flower mechanism agrees with that of T. arvense. 



