6 MINNESOTA STUDIES IN PLANT SCIENCE 



follicles are erect at maturity and united either near the base or up to the 

 middle. In Calthophyllum the carpels are entirely distinct and are spread 

 apart as they increase in size, while the gland takes the form of a broad 

 zone surrounding the basal portion of the carpels. There are also outstand- 

 ing differences in the young carpels of these sections (Plate I). 



On the other hand there is a series of sections in which the receptacle 

 is more or less united with the ovary. This condition has been termed 

 "subinferior." Four sections comprise this series, namely, Dermasea' 

 ChionophUa, Micranthes, and Trkarpum.'' The carpels are in all cases 

 distinct to the base but are connected laterally by the adnate receptacle 

 and at least the lower portion of the gland. The sections may be grouped 

 into two divisions according to the number of carpels. Thus in Tricarpum 

 the number is uniformly three, although four are sometimes found. In the 

 remaining sectio-ns the number two is quite constant. The section Dermasea 

 possesses a very distinctive gland which is in the form of a fleshy ring around 

 the basal portion of the carpels in species having a very shallow receptacle. 

 In ChionophUa and Micranthes the glands are in the form of a broad fleshy 

 and prominent disc, closely appressed to the base of the calyx in ChionophUa, 

 but considerably elevated in Micranthes. In Tricarpum the gland is very 

 similar to that of Micranthes but is only slightly elevated. In both Micran- 

 thes and Tricarpum the margin of the gland persists as a conspicuous flange 

 on the sides of the carpels. The species are readily referred to their respec- 

 tive sections on the characters of the gland. There is considerable variation 

 in the depth of the receptacle in Dermasea, where in exceptional cases 

 {Saxifraga nivalis) it is united to the carpels for about half their length. 

 This variation occurs in certain species of the section Micranthes, as for 

 example Saxifraga pennsylvanica and S. oregana, in which this condition 

 often gives the appearance of distinct hypogyny. The receptacle in Chiono- 

 phUa, Micranthes, and Tricarpum is characteristically deep. 



The second division comprises only two sections, Arabisa, and Heterisia. 

 In both, the ovary is wholly superior and the carpels united about to the 

 middle. The carpels and glands indicate two distinct lines of evolution. 

 In Arabisa the young carpels are erect and broadly conical, terminating 

 above in mere peglike beaks, while the gland has the form of a narrow 

 girdle immediately above the base of the carpels. In Heterisia the carpels 

 are strongly contracted above into slender, strongly divergent beaks, and 

 are surrounded for the greater part of their length by a thick fleshy gland. 



'Dermasea (Haw.) sect, nov., Dermasea Haw., Saxif. Enum. 45. 1821, as genus. 



'Tricarpum sect, nov., receptaculum ovario alte adnatum; carpidia tria distincta, receptaculo 

 et supra glandula conjuncta; folliculi crassi inflati stylis crassis divergentibus rigidis, stigmatibus 

 discoideis; clandula crassa ex calycis basi breviter clavata, marcine ir.fcriore persisttnte; filamenta 

 subulata; sepala patentia. 



