NORTH AMERICAN GERANIACEAE. 



97 



Table III. O. Suksdorfii. 



Table IV. Pollen of O. Suksdorfii." 



as if the.se might be the persistent long-styled form of originally trunorphic ancestors- 

 But as the pollen of the two sets of stamens does not show the differentiation that would 

 be expected in that case, it is more probable that they are to be compared with the still 

 undifferentiated and homogone O. corniculata. 



In all of our species the flowers are adapted to pollination by bees, which are attracted 

 by their conspicuous color, and usually directed by veins of a deeper shade to a more or 

 less abundant supply of nectar secreted by a series of small glands at the bases of alter- 

 nate stamens, on the outside. This is generally protected from rain and dew by the 

 hairiness of the longer stamens or styles, as well as by the closing of the flowers at 

 night and in cloudy Aveather. O. corniculata and 0. acetosella, the only cosmopolitan 

 species, apparently owe their extensive distribution to the facility with which they are 

 self-fertilized. The small flowers of the former are freely self-fertile, although they are 

 visited and intercrossed by small bees in sunny weather, presumably with benefit to the 

 species ; and the latter produces reduced but extremely fruitful cleistogamous flowers 

 on pedicels that are concealed at the base of the jjlant^. 



AVhile the j^orth American species deviate very little from the open funnel shape that 

 appears to be typical of the genus, this is not true of all species. The corolla of O. 

 macrostylis^, for example, a South American species, is lengthened into a slender tube 

 2 X 15-25 mm., a modification which clearly adapts the flowers to pollination by lepidop- 

 tera. (Note 10.) 



Oxalis is a genus with explo.sive fruit. (Xote 11.) At maturity the carpels dehisce along 



' la both tables of pollen measuremeiiUs, the shorter 

 diameter of freshly swollen grains from herbarium spec- 

 imens Is given. 



* According to Hildebrand (Lebensvcrbaltnisse, 22) 0. 



Oreyana, in cultivation, produces only open flowers through 

 the entii'e season. 



^ Jacquin : Oxalis Monogr., Pis. 9-12. On this species, 

 see further Walpers, Ilepertorium, i, 477 ; and Uiklebraud : 

 Monatsber. Berl. Akad., 186G, 361-2. 



