346 MR. F. N. WILLIAMS ON THE GENUS DIANTHUS. 



I found them floating in the Lea and the Thames in January, &c. 

 Lemna trisulca seems to live through the winter in the Lea and 



* 



Thames. After many weeks of frost in the winter of 1890-91, 

 I found it in January inclosed in quantity in the ice of an Epping 

 Forest pond. The fronds of L. gibba, polyrrhiza, and trisulca 

 behave like those of L. minor both in sea-water and when 

 dried. 



A Monograph of the Geims/Dianthus, Linn. 



By F. N. WilliaVs, F.L.S. 



[Eead 4th February, 1892.] 



Most of the species oiDianthus are perennial; a few are annual, 

 or even biennial. The csespitose habit of many of the perennial 

 species is due to the development of dense and leafy barren shoots, 

 in which the internodes are almost suppressed. The rootstock 

 produces barren shoots and ascending flowering stems. The 

 stems are either terete or angular, i. e., they may assume a 

 cylindrical or prismatic form ; in the latter case the number ol 

 the angles bears a definite relation to the phyllotaxis. As the 

 leaves are opposite and decussate, stems that are not cylindrical 

 have four angles, and the acuteness of the angles determines the 

 furrowed condition of the surface. Angular stems are more 

 frequently than not glabrous. Throughout the genus the nodes 

 are well-developed, and such as to give the stem and its branches 

 a jointed appearance; this is the more marked from the fact that 

 the lamina springs direct from the stem without any intervening 

 petiole. The internodes, which are almost suppressed in the 

 barren shoots, in the flowering stems seem to bear some sort ot 

 relation to the leaves borne upon them, being sometimes equal 

 in length to the leaves, sometimes double the length, and the 

 ratio seems to obtain to the apex of the stem, where both inter- 

 nodes and leaves become shorter. Examples of shortened inter- 

 nodes are seen in the rosette of leaves at the base of the stem ot 

 D. Caryophyllus, in the fascicled leaves of the barren shoots ot 

 D. plumarius, and generically in the squamiform leaves beneatn 

 the floral organs. In the flowering stems of D. longicaulis the 

 nodes are very distant. Since the intercalary growth is at its 

 maximum, and persists longest at the base of each, in Dianthu* 



