26 CHLORIS BOREALI-AMERICANA. 



tion ; and the intervening space is partially filled by a little very 

 loose and filmy cellular tissue. The inner portion of the parietes is 

 much thicker and more fleshy than the outer ; it commonly presents 

 four equidistant projections or folds, which partially divide the 

 cavity in a cruciate manner ; but occasionally one of these, or two 

 opposite ones, are partially or altogether wanting. These four 

 placentiform folds may be directly compared with the four nearly 

 equidistant placentae of Anoplanthus (Orobanche) unijlorus, with 

 which they agree in position; that is, two of them are borne on the 

 face of each carpel, about half way between its edges (marked by 

 the line alternating with the stigmas) and the axis (where the 

 midrib is represented by a slender line or cord of vessels, shown 

 in the middle of Fig. 12, which may be traced upwards through 

 the style to the stigma) ; so that they might be taken for sub- 

 marginal half-placentas. But here we find a further peculiarity in 

 Obolaria, namely, that not merely these placenta-like processes, 

 but the whole lining of the cell, is equally and uniformly ovulifer- 

 ous ! Of this, no parallel instance is known, I believe, in a uni- 

 locular compound ovary, although it occurs in a few plants with 

 apocarpous ovaries, and in one small family (Nymphaeaceae) with a 

 compound multilocular fruit ; but to none of these does Obolaria 

 exhibit any other points of similarity. 



The want of much cohesion, except at the sutures, between 

 what I have called the outer and the inner parietes of the ovary 

 naturally suggests another possible explanation of the anomalous 

 placentation of Obolaria ; namely, that the inner ovuliferous portion 

 may consist of a pair of concave placentae, completely lining the 

 ovary, much as in Hydrophyllum, but perfectly united where their 

 edges come in contact, and ovuliferous throughout their whole 

 sinuously biplicate inner face. But no trace of such union can be 



