THE RELATION BETWEEN THE GENERA THYSANELLA AND POLYGENELLA AS SHOWN BY A HITHERTO UNOBSERVED CHARACTER.
The genus Thysanella has generally, and apparently without good reason, been included in Paygonztin.
In a former paper* I stated that Tkysaizella was a perfectly distinct genus, related to Polygonella and not to Polygonum.
A glance at Thysanella fimbriata and 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 Thysanella 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 Polygonum 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 genera Thysanella and Polygonella which is possessed by no other member of the family Polygonaceae. In the * Mem. Dept. Sot. Col. Coll. i : 9.
one species of Thysanella and in all the species of Rillyonello the branching is not nodal, but internodal.
The internodal branching is brought about by the adnation of a secondary axis to a primary axis for a greater or less distance above a secondary node, usually about one-half the distance from node to node. The true condition is more plainly shown in Thy sanella, where the union of the two axes is not as complete as in Polygonella, a shallow but usually distinct groove showing the place of union.