100 . WILLIAM TRELEASE ON THE 



on the lower petal and the floor of the saecate sepal, and touch anthers or stigma with 

 their backs while feeding on the nectar. Bennett, the only one who has carefully studied 

 the flowers from this standpoint, has shown that the appendages on the inner side of the 

 filaments form a hood which, in conjunction with the jiendent position of the flowers, ef- 

 fectually prevents self-pollination. The nectar spurs are frequently perforated by hum- 

 ble-bees, and hive-bees subsequently make use of these perforations to abstract nectar. 

 Delpino has shown that some exotic species are apparently iDoUinated by lepidoptera, — 

 the long-s2>urred /. Sultana, which is now extensively grown as a greenhouse or border 

 plant, is evidently of this class, and according to Baillon, /. Ilumblotiana, of Madagascar, 

 is ornithophilous. It should be noted also that humming-birds are not infrequent visitors 

 to our own /. fulva. Both of our species bear regular cleistogamous flowers on the 

 axillary peduncles, and the greater part of their fruit results from the fertilization of 

 these reduced flowers, which are very abundant. 



The ripening capsides are in a state of tension Avhich finally results in the outer part 

 of the valves breaking away below from their septa, which remain, with the seeds, at- 

 tached to the persistent axile column. The liberated valves then rapidly coil up, strip- 

 ping or shaking oft" the seeds as they do so, and often throwing them to a considerable 

 distance from the plant. (Note 12.) 



The tribe Pelargonieae, which is not represented in our district, but is well knoAni in 

 the cultivated ^'geraniums" (^Pelargonium) and nasturtion {Tropaeolum) , possesses some 

 interesting peculiarities connected with pollination, which can only be indicated in the 

 briefest outline here. The flowers are protandrous, with one sepal produced as a long 

 spur that is adnate to the pedicel in the former, and free in the latter genus. The epi- 

 dermis, lining the narrow cavity of this spar, is provided below with short, unicellular 

 hairs, the walls of which are thickened in a peculiar manner at the apex, the interior of 

 the swollen tip finally undergoing a mucous degeneration connected with the secretion 

 of nectar. Occasionally the cavity of the spur is double in Pelargonium, and in abnor- 

 mal cultivated forms it sometimes disappears; the Avell-marked veining of the, iipper 

 jjetals, which serves as a nectar-mark, then disappearing also, as Mr. Darwin has shown. 



In Pelargonium zonule, etc., the flowers are well adapted to pollination by butterflies. 

 Owing to their lateral position, their petals are unequal, as has been shown to ]je the 

 case in Erodium. This irregularity is somewhat intensified in the common "rose-gera- 

 nium" (-P. graveolens) , and very much so in P. tetragonnm, etc., the flowers of which 

 Delpino has not inaptly compared with the papilionaceous type of Leguminosae. Not 

 a few species of this genus are nearly scentless during the day, but extremely fragrant 

 at night, and in this and other peculiarities indicate adaptation to cross-fertilization by 

 nocturnal moths. Tropaeolum, with numerous species, presents a series ranging from 

 such as are bee-pollinated to others which are as clearly ornithophilous. (Note 13.) 



