CRUCIFERAE 



83 



54. Arabis L. 



Flowers usually small, seldom of considerable size; white or whitish, rarely 

 rose-red or lilac or blue ; generally homogamous, infrequently protogynous. Nectar 

 half-concealed; nectaries 2, 4, or 6. 



182. A. alpina L. (Sprengel, 'Entd. Geh.,' p. 333; Axell, 'Om Anord. for 

 Fanerog. Vaxt. Befrukt.' ; Herm. Miiller, ' Alpenblumen,' pp. 143-4; Schulz, 'Beitrage,' 

 II, pp. 1 1-2.) The flowers are homogamous. Of the four nectaries those outside 

 the bases of the two short stamens are the largest; their nectar collects in the 

 dilatations of the sepals beneath them. The two smaller nectaries outside and 

 between the bases of each pair of long stamens, secrete hardly any nectar. The 

 form of the nectaries is very variable. The long stamens sometimes turn their 

 pollen-covered sides towards the adjacent short stamens, so that an insect probing 

 for nectar must touch them, and therefore cross-pollination is likely to take place. 

 In other cases these stamens turn towards the stigma, and then, especially in dull 

 weather (and always in Greenland), either pollen falls from them on the stigma, or 



Fig. 29. Arabis alpina, L. (after Herm. Muller). A. Flower after removal of two petals, seen from 

 the side ; sA, nectar receptacles. Each of the long stamens is turned towards the adjacent short stamen. 

 B. Flower seen from above. The pollen-covered sides of all the anthers are turned towards the stigma ; 

 the filaments, however, are curved back in such a way that self-pollination does not take place at this 

 stage. C. Flower after removal of calyx and corolla : n, functional nectaries ; ', vestigial nectaries. 

 Stamens are as in B. ( x 7.) 



else this is touched by the anthers, so that automatic self-pollination is effected. In 

 Nova Zemlia, according to Ekstam, the feebly odorous flowers are 6-12 mm. in 

 diameter, and protogynous-homogamous. Nectar is abundantly secreted, and self- 

 pollination is easily possible. (See Fig. 29.) 



This species was observed in flower, and bearing young fruits, in Spitzbergen on 

 July 29, 1896 (Anderson and Hesselman, 'Bidrag till Kanned. om Spetsbergens o. 

 Beeren Eil. Karlvaxtflora,' p. 34). 



Visitors. Herm. Muller observed 2 flies in the Alps ; while Schulz in the Tyrol 

 also saw various butterflies. MacLeod noticed 2 flies in the Pyrenees; and Loew 

 in the Berlin Botanic Garden saw the hive-bee sucking nectar. 



183. A. Hookeri Lange. This species is native only to West Greenland and 

 Arctic America. The white petals are as much as 5 mm. long, and project beyond 



G 2 



