HEP A TIC.E. 



307 



depression in the thalloid forms, as well as on the termination of the filiform stem 

 in the leaf-bud of the foliose genera. The form of the apical cell, and its segmen- 

 tation in the thallus of Metzgeria, have been represented in detail in Figs. 99 and 100 

 (p. 120) ; in Aneura and Fossombronia it is also wedge-shaped. In Blasia, on the other 

 hand, Leitgeb states that it is four-sided, and forms four rows of segments, a dorsal, a 

 ventral, a right, and a left row. ' This may be most easily represented by supposing a 

 wedge-shaped apical cell forming segments by walls inclined alternately upwards and 

 downwards (towards the dorsal and ventral surfaces), as well as lateral segments from 

 which the leaves proceed ; a leaf is produced from the dorsal part of a lateral segment, 



Fig. 22T. — Female receptacle of Marchantt.i poly- 

 morpha seen laterally from below; st stalk with two 

 channels ; sr the radiate outgrowths of the disc ; 

 pc the "intermediate perichxtium ; / sporogonia 

 (X about 6). 



Fir,. 222. — Marchaiitia polymorpha ; A vertical section through a female receptac.e hn, bb leaves ; h root-hairs in its 

 channel ; i: large cells between the air-cavities of the upper side ; /.' horizontal section of half an older receptacle and of 

 its stalk St; chl the chlorophyll-bearin^^ tissue of the disc. Iarg:e hyaline cells ; /c the common perianth leaves (/<: in 

 Fijj. 221) ; a unfertilised archegonia ; pp involucres of fert.Iised archegonia ; C vertical longitudinal section through the 

 receptacle; a two archegonia ; /r general involucre of the arciiegonia, or perich^tiiim. 



a kind of leaf-tube from its central part, and a second leaf from its ventral part, though 

 this last is more often absent ' (Leitgeb, in lit.). It has already been mentioned that 

 Leitgeb supposes this to be the mode of apical growth in those cases, like Pellia, 

 where Kny thought he saw a ro^ of apical cells. 



In the Jungermannieae with filiform stem and leaves arranged in two or three 

 rows, the stem ends in a three-sided apical cell which forms three rows of segments 

 in spiral succession ; two rows being dorsal and lateral, while the third row forms the 

 under or ventral side of the stem. The successive septa of each row of segments are 

 parallel to one another, but the segments themselves are in straight rows, the rows being 



X 2 



