102 



MOSSES AND FERNS 



CHAP. 



rhizoids to* the substratum, there is a row of much smaller 

 leaves (amphigastria), more or less irregularly disposed. The 

 dorsal leaves, seen from above, are nearly oval in outline, but 

 each has a smaller ventral lobe, pointed at the tip, and closely 

 appressed to the lower surface of the much larger dorsal lobe. 

 The ventral lobes closely resemble the amphigastria, both in 

 form and size, and with the latter form apparently three rows 

 of leaves upon the ventral side of the stem. The structure of 

 the leaf is of the simplest character, consisting of a single layer 

 of polygonal cells containing numerous chloroplasts. 



The plants grow 

 where they are exposed 

 to alternate wetting and 

 drying up. They may at 

 any stage become com- 

 pletely dried up, and on 

 being moistened will re- 

 sume at once their ac- 

 tivity. In the dried con- 

 dition, the species under 

 consideration often re- 

 mains for several 

 months without appa- 

 rently being injured in 

 the least, and this power 

 is shared to a consider- 



FiG. 49.— Porella Bolanderi. A, Female plant, X4; ^^ablc degree by mOSt of 

 5, archegonial branches; E, an open sporogo- the aCrOgyUOUS formS, 

 nium, X4; C, a male plant, X4; r?> the an- •• ,. ., 1 1 •, , 



theridiai branches. whosc favourite habitat 



is the trunks of trees. 



The apical growth of the stem is extremely regular, and as 

 in ail the other acrogynous Hepaticse, the apical cell is a three- 

 sided pyramid (Fig. 50, A). In longitudinal section it is 

 much deeper than broad, and its outer face is almost flat. In 

 cross-sections (Fig. 50, B) it has the form of an isosceles tri- 

 angle, the shorter side turned toward the ventral surface of the 

 plant. From this cell three sets of lateral segments are cut off, 

 two dorsal and one ventral, and "each of these gives rise to a 

 row of leaves, a leaf corresponding to each segment of the 

 apical cell. The first division wall in each segment is at right 

 ; angles to its broad faces and divides it into two cells of some- 



.s. 



