NOETH AMERICAN GERANIACEAE. 95 



posed trimorphic species {0. violacea) , and observing only long- and short-styled jalants, 

 I made measurements of the flowers of many plants, but found only these two forms, al- 

 though the plant is very abundant and a native species. I have since examined a great 

 many more plants about Madis(jn, Wisconsin, in the vicinity of St. Louis, Mo., and from 

 central Illinois, without finding a single mid-styled flower; and my correspondents who 

 have paid attention to the subject have had the same experience. N^umerous hei-bari- 

 um specimens, representing nearly the entire range of the species, are also all long- or 

 short-styled. From a careful consideration of these facts, T have been convinced that 

 this species has become dimorphic from the suppression in some manner of the mid- 

 styled form, for it cannot be doubted that it is descended from originally trimorphic pa- 

 rents, since the stamens are still in two remote sets, not as yet coml^irfed in a sin^-le set, 

 though in flowers of both sorts they apjiear to be somewhat closer together than they 

 should be in a trimorphic species. Mr. B. M. Yaughan, who studied O. violacea in my 

 laboratory some j^ears since, thought that he detected an abortion of the pollen of the 

 mid-stamens in both long- and short-styled flowers, indicating a loss of function that 

 might be held as indicative of their ultimate disappearance. IIoav far this may be true 

 I do not know. Mr. Darwin, to whom some of these facts were communicated shortly 

 before his death, also thought that this might be a trimorphic species becoming or be- 

 come dimorphic^ I may add that our other species of the violacea group are found only 

 under these two forms in herbaria, so far as I have examined them; but Hildebrand has 

 cultivated the mid-stjded form of O. vespertiUonis^. 



Our yellow-flowered caulescent species of the corniculata group are more puzzling 

 than those which have just been considered. In the tyjjical smaller-flowered form of 

 0. coniiculata and its variety stricta, the styles are a little shorter than, or about equal to, 

 the longer stamens, and the flowers are unquestionably homogone''. But in the common 

 villous St. Louis plant, Avhich is regarded as a form of var. sfricta, the flowers are larger 

 and the pistil appeai-s to have increased in length correspondingly with the petals, as may 

 be seen from the following measurements, from the base of the flower (Table I). These 

 flowers might be taken for the long-styled form of a trimorphic species ; but the pollen- 

 grains from both sets of stamens are essentially of the same size, so that this theory is 

 untenal)le^, and both corniculata and this variety are to be regarded as merely variajjle 

 in the relative length of stamens and pistiF. 



There are also numerous stipulate specimens which could be referred to O. corniculata 

 in the broad sense in which that species is understood, if it were not that they are still 

 larger-flowered and may be trimorphic. I append some measurements of the stamens 



' As I stated in the American Natui-alist, in 1SS2, Hikle ^Lebensverhiiltnisse dev Oxalisarten, 3G. 



brand fMonatsber. Berlin. Akad., 18fi6, 357, — and recently ^See Hildebrand: Monatsber. Berl. Al^ad., ISfifi, 308; 



in Bot. Zeitung, 1887, 22) reports one mid-styled specimen Bot. Zeit., 1887, 37. 



of O. riV<;i7''ea, withont locality, in the lierbai'ium of Alex- ■'Hildebrand (IMonatsber. Berl. Akad., ISBO, 368-3) 



ander Brauu ; and a figure of a mid-styled flower of what found one long-styled specimen of stricta collected by 



is called O. violacea is given by Payer (Organogenie, PI. Treviso (but without indication of locality), and one from 



11, flg. 10, — copied in Luersseu's Haudb. Syst. Hot., 11, Missouri, while a specimen from Kentucky is said to be 



168). I also find several mid-styled specimens under this short-styled. 



name, from about Buenos Ayres, in the Gray herbarium, * See Darwin's Different Forms of Flowers, 181. 

 but they are not our North American plaut. 



HEHOIRS BOSTO.N SOC. NAT. HIST., VOL. IV. It 



