344 



PART III. THE CLASSIFICATION OF PLANTS. 



occasionally from the amphigastria (e.g. Lejeunia, Frullania, Mastigobryum, 

 Lepidozia, Lophocolea, etc.) : they are absent in Trichocolea; and in Eadula 

 they are developed on the convex surface of the lower lobes of the lateral 

 leaves. 



In the radial foliose forms, the leaves are borne in three rows in Haplomit- 

 rium, and in two rows in the radial species of Riella (helicophylli and Parisii) ; 

 here there is no distinction of amphigastria. Root-hairs are absent in Haplo- 

 mitrium, their functions being discharged by root-like branches : in the above 

 species of Riella the root-hairs are borne on the swollen basal end of the stem. 



Papilla bearing glandular hairs, secreting mucilage to moisten the growing- 

 point, are very generally developed ; they are transitory, and are therefore only 

 to be found near the growing-point. In the dorsiventral forms they are de- 

 veloped mainly on the ventral surface, either as appendages of the amphigas- 



tria or (as men- 

 tioned above) as 

 representing 

 them in those 

 forms in which 

 the amphigastria 

 are wanting or 

 rudimentary. In 

 the foliose forms 

 similar papillae 

 are also developed 

 as appendages of 

 the young lateral 

 leaves ; notably in 

 the radially sym- 

 metrical genus 

 Haplomitrium. 



The growth of 

 the shoot is 

 effected by an 

 apical growing- 

 point which pos- 

 sesses (except 

 perhaps in Blasia 

 and Pellia, in 

 which tbere ap- 



FIG. 243. Growing-point of thallus of Metzgeriafurcata. t Apical 

 cell; s' etc., successive segments; m' m" marginal cells; p' super- 

 ficial cell ; i i cells of the midrib ; c clavate hairs. ( x 540 : after 

 Strasburger.) 



pears to be a group of initial cells) a single apical cell. The apical cell of the 

 thalloid forms is most commonly two-sided (Fig. 243) ; the base is directed 

 outwards, the apex inwards, and from the two sides segments are cut off alter- 

 nately right and left. The apical cell of the foliose forms, with the exception 

 of Fossombronia and Riella which have a two-sided apical cell, is a three-sided 

 pyramid ; its base is directed outwards, its apex inwards, one side is ventral 

 and the other two are dorso-lateral ; this latter statement does not, of course, 

 apply to Haplomitrium. In Blasia and Pellia cell-division in the growing- 

 point appears to take place much as in the Marchantiacese. 



