110 HOFMEISTER, ON 



rounded by a process of cell-formation which appears 

 very similar to that by which the cells of the very young 

 gemmae of Marchantia increase in breadth (PL XVI, fig. 

 13). The cell-multiplication on the side of the leaf furthest 

 from the median line of the shoot soon exceeds that of the 

 other side, causing the one-sided appearance which is 

 usual in the leaves of Marchantia. The cell-multiplication 

 is arrested at the apex, whilst it continues at the base. 

 Many of the marginal cells grow into crooked, short, bi- 

 cellular, clavate hairs, similar to those which are found close 

 under the fore edge of rapidly growing shoots of Pellia, as 

 well as in the young parts of many other Jungermanniae. 

 Individual cells, arranged at definite distances on the 

 margin, multiply for a longer period than their neighbours, 

 by which means the leaf soon becomes angular. 



The development of the leaves of Targionia, Rebouillia, 

 Lunularia, and Marchantia, appears not to differ essentially 

 from the above. In Marchantia polj/morpha even the 

 leaves exhibit the tendency, common in these plants, of 

 sending out from the margins of their vegetative organs 

 dentate, chaffy processes, a tendency which is seen on 

 the marginal scales on the edges of the bud-receptacles 

 on the perichaete and perigone. By these processes the 

 leaves are beautifully fringed. 



The well known characteristic structure of the flat stem 

 of the Marchantieae is marked by the separation of the 

 tissue of the stem into first, an inferior layer of large, 

 very elongated cells, without intercellular spaces; secondly, 

 a layer superimposed upon the latter layer, and con- 

 sisting of moniliform rows of cells, separated by wide 

 air-cavities and rich in chlorophyll, which layer is di- 

 vided into partitions by rhomboidal, cellular walls, each 

 consisting of a single stratum ; and, lastly, an epider- 

 mis with transparent cell-contents, covering the latter 

 layer, which is in close connexion only with the cellu- 

 lar walls just mentioned, and is pierced by a stomate 

 of peculiar structure at the middle point of each of the 

 partitions of the underlying layer. The foundation of 

 this peculiar structure is laid at a very early period. 

 At a little distance behind the punctum vegetationis of 



