HOFMEISTER, ON THE HIGHER CRYPTOGAMIA. 103 



and structure. The longitudinal growth of each shoot 

 is caused by repeated division in its apical cells, by means 

 of alternately inclined septa (Lunularia, PL XV, fig. 19; 

 Eegatella, PL XVI, fig. 3). Soon after the first division of 

 this kind has taken place in the mother-cell of a new 

 shoot (which mother-cell lies at the bottom of the axil 

 of two older shoots), the number of the apical cells is 

 doubled by the appearance of a longitudinal septum 

 (PL XVI, fig. 2). The fore edge of the shoot widens 

 continually during and until the cessation of its longitu- 

 dinal development, by means of repeated division of the 

 apical cells by longitudinal septa ; this increase in breadth 

 is more or less rapid, according to the circumstances under 

 which the plant is growing, and according to the species 

 of plant. The differences in habit in different species, as 

 well as in individuals of the same species growing under 

 different circumstances, depend, in the first place, upon 

 whether the lateral margins of the new shoots amalgamate 

 with the adjoining lobes of the fore edge for a considerable 

 length, or not. Those shoots of Pegatella and of 

 Rebouillia w T hich are formed late in autumn, which remain 

 quiescent during the coldest part of the year, and develope 

 themselves in early spring, remain completely separated 

 from the projecting portions of the shoots of the previous 

 year ; this is the cause of the jointed appearance of the 

 leaf-like stem of these species. In Marchantia, in Targionia 

 under all circumstances, and in the summer shoots of 

 Pegatella and Rebouillia, the amalgamation is, on the other 

 hand, very complete. In the next place, differences of 

 habit depend also upon the length of the lines of amalga- 

 mation of the three shoots which combine to form one 

 shoot. In Pegatella, and in specimens of Marchantia poly- 

 morpha and Lunularia vulgaris, which grow in very moist 

 places, the amalgamation is far more considerable than in 

 specimens of the same species from dry habitats,* or than 



* The length of the amalgamation is manifestly to be measured by the 

 number of cells, and not by lines and inches. The expansion of individual 

 cells has the greatest influence upon the absolute length of the shoots. The 

 latter becomes quite enormous when new shoots of Marchantia polymorpha, 

 covered by older portions of the mother-plants, are making their way to the 

 light. 



