47 



genus. Notwithstanding these exceptions, the species for the 

 present must be referred to Aviadaria and forms the first excep- 

 tion to its normal morpliology as far as I have observed, and an 

 interesting one. 



Hxplanatlon of Plate 293. 



1. Whole plant, natural size. 



2. Leaf, enlarged. 



3. Flower, enlarged. 



4. A stamen, enlarged. 



5. Achene, enlarged. ' 



6. Cross-section of achene, enlarged. 



The Relation between the Genera Thysanella and Polygenella as shown 

 by a hitherto unobserved Character. 



By John K. Small. 



The genus Thysanella has generally, and apparently without 

 good reason, been included in Polygoiuun. 



In a former paper •* I stated that Thysanella was a perfectly 

 distinct genus, related to Polygonella and not to Polygonum. 



A glance at Thysanella Jiinbiiata dixxd any member of the genus 

 Polygonella ought to be sufficient to convince any one of the strong 

 relationship between the two genera. The habits of the two are 

 almost identical, while the vegetative organs of TJiysanella much 

 more closely resemble those of Polygonella than they do any 

 member of Polygonum. 



Coming to special morphological characters let us first con- 

 sider the flower. Here we find the special development in the 

 inner series of sepals ; likewise in Polygonella it is the inner sepals 

 that develop special organs. In Polygonjim the outer sepals are 

 specialized if any development at all takes place, the inner series 

 being practically unmodified. 



Besides the foregoing considerations I have lately noticed a 

 character in both the geneia Thysanella and Polygonella which is 

 possessed by no other member of the family Polygonaceae. In the 



* Mem. Dept. Bot. Col. Coll. i : 9. 



