MEMOIRS FROM THE DEPARTMENT OP BOTANY OF COLUMBIA COLLEGE. 9 



generic validity of such individuals or groups as Thysanella, Polygonella and Fagopyrum. 

 Linnaeus included the latter two groups under Polygonum, the former not being known 

 in his time. In my opinion all three form perfectly good genera. We have excellent 

 characters in the case of Fagopyrum. This type resembles Polygonum in its habit more 

 than the other two forms in question, but its tissues have a characteristic texture and its 

 leaves a distinctive shape. The most important differences, however, exist in the flower 

 and fruit. The calyx withers, or remains unchanged in fruit, the faces of the achene 

 are pinnately striate and the angles more or less margined or crested, and the embryo 

 is central, the broad cotyledons almost dividing the mealy albumen into halves by an S- 

 shaped curve. None of these characters are possessed by Polygonum. In Polygonella 

 we find a very strong character in the habit of the species, and they all possess it in about 

 the same degree. Here again the flowers furnish characters to separate this type from 

 Polygonum. In the first place, the pedicels are normally solitary, whereas in Polygonum 

 they are fascicled, and secondly the calyx either remains unchanged or the three inner 

 segments develop into conspicuous wings in fruit, two characters not belonging to Poly- 

 gonum. Thysanella has good characters, but as we are not directly concerned with it, 

 suffice it to say that its affinities are closer to Polygoiiella than to Polygonum, and as the 

 former genus is distinct from the latter, if Thysanella could not stand generically distinct 

 it would naturally fall into Polygonella and not into Polygonum. 



Polygonum proper therefore consists of herbaceous or shrubby plants, often con- 

 spicuous on account of their prominently jointed stems. They are either terrestrial, 

 amphibious or aquatic, and their vegetative organs may be glabrous, glaucous, variously 

 pubescent or glandular. Some species are annual, others are perennial by means of large 

 roots, creeping stems or rootstocks. The roots are variable in size, sometimes slender and 

 fibrous, often large, fusiform and woody. In dry clay soil the development is usually 

 restricted, while in sand they often elongate to a remarkable degree. The subgenus Bis- 

 torta furnishes two kinds of fleshy rootstocks ; the one is bulb-like and the other more or 

 less elongated, either creeping or horizontal. The texture of the tissues of the stems 

 varies from herbaceous to woody, and the habits it has assumed are manifold. . Some are 

 erect or prostrate, some float in or on the water, others climb by means of recurved prick- 

 les, and still others are scandent by twining stems. They may be strict or flexuous, in 

 most cases unarmed, in a few furnished with strong recurved prickles, and the internodes 

 appear as terete in some cases, in others they are channeled or ridged, while in many 

 species they are gradually or abruptly enlarged towards the nodes, a character so prom- 

 inent in this genus. The leaves are alternate and follow in a I or rarely in a I spiral. 

 They vary much, like the other vegetative organs, in their texture and shape, the bases 



