BRYOPHYTA 



179 



Vegetative propagation in the Anacrogynae occurs by death of the 

 older parts of the thalkis, resulting in the isolation of branches. Also, 

 gemmae are produced in certain genera, such as Riccardia and Metzgeria, 

 while others produce tubers that live over from one growing season to the 

 next. 



Sex Organs. The antheridia and archegonia are borne either on the 

 same gametophyte or on separate gametophytes, according to the species. 

 They are always dorsal in position, generally occurring singly or in groups 



Fig. 146. Thallus of Pellia epiphylla (A) with a mature sporophyte, of Pallavicinia lyellii 



oi i-euia epipnyua (A) wiiu a mature ot^v^n^i^.»j vy^, v^^ j. ^^v,a,u^„.v^^ „yi^i^„ 

 (B) with two groups of archegonia, and of Syrnphyogyna brongniartii {C) with three groups 

 of archegonia, twice natural size. 



on the main thallus or, less frequently, on special short branches that in 

 Riccardia are lateral and in Metzgeria are ventral in origin. The sex 

 organs, unlike those of the Marchantiales, are never borne on stalked 

 receptacles. The archegonia are usually protected by an involucre. 

 The antheridia are protected in various ways: in Metzgeria, by incurving 

 of the thallus; in Riccardia and Pellia, by upgrowth of adjacent tissues; 

 in Pallavicinia and Syrnphyogyna, by a special involucre. 



In the Jungermanniales the development of the antheridium is char- 

 acteristic, differing considerably from that seen in the Marchantiales and 

 Sphaerocarpales. The antheridium arises as a papillate initial that 

 undergoes a transverse division (Fig. 147 A). Another transverse wall 

 usually appears in the outer cell, but the third wall is a median vertical 

 one (Fig. 1475, C). In each of the two terminal segments thus formed a 

 periclinal division takes place. Two additional periclinal walls then come 

 in at right angles to the first ones, intersecting both these and the median 

 wall. As a result, four primary wall cells are cut off from two central 



