107] NORTH AMERICAN AND WEST INDIAN CUSCUTA—YUNCKER 17 



but with the stigmas somewhat flattened. One or two species show 

 stigmas somewhat irregular and convoluted. All of the species found so far 

 in this country with the linear type of stigmas are Old World forms that 

 are parasitic on economic plants. C. europaea has been found but three 

 times in this country according to the records, and its apparent scarcity 

 is probably because of the fact that it does not ordinarily parasitize crop 

 plants and is unable to gain a foothold. The stigmatic characters are 

 easily seen without dissections and are the most constant to be found in 

 the flowers. These, with certain other characters, in correspondence 

 with geographic distribution, seem to indicate the natural division of the 

 group into its primary subdivisions. 



The two carpels making up the capsule are not completely united in all 

 the species. An opening extends down between the styles into the capsule 

 in the most of them, but not, however, connecting with the interior of the 

 cells. The size and depth of this opening, which Engelmann termed the 

 "intrastylar aperture," is somewhat different for the various species. 



The capsule may or may not be circumscissile, depending upon the 

 species. The Old World forms, as well as most of those from Mexico and 

 the southwestern part of the United States have capsules that open by a 

 more or less regular line of cleavage towards the base. In some species a 

 thickened ridge is formed which marks this line of separation. Most of 

 the species, however, do not show this thickening, and, while the cleavage 

 is ordinarily quite regular, in some species it is somewhat ragged. The 

 partition wall composed of the adjacent walls of the two carpels up to 

 the place where the intrastylar aperture begins is frequently left in the 

 basal portion of the circumscissile capsule after opening. This is usually 

 obcordate and is most admirably exhibited in C. applanata and C. epilinum. 

 It may be somewhat difficult to predict the mode of dehiscence when 

 examining young flowers, but with those with more mature capsules a slight 

 pressure with the point of a pencil will usually cause the circumscissile 

 type of capsule to break loose, while the non-circumscissile type will be 

 crushed or will tear irregularly. In a careful dissection of young flowers 

 of those species possessing a circumscissile type of capsule the ovary may 

 often be detached if pulled, since the base ordinarily forecasts the line of 

 circumscission of the mature capsule in having a weaker zone. The shape 

 of the capsule is characteristic for the different species. It ranges 

 from globose-depressed (C. polygonorum, C. umbellata, etc.) to globose- 

 ovoid (C. salina, C. denticulata, etc.) or pointed (C. gronovii) or long- 

 beaked, flask-shaped (C. rostrata). This variation in shape is due in some 

 species to a thickening of the capsule wall at the apex (C. gronovii) but 

 in others (C. denticulata) this is not true. Many species have the capsular 

 wall thickened in the form of a ring or collar about the style bases and 

 bordering the intrastylar aperture. 



