J UNGER MA NNIEA E. 



155 



Both the main and the lateral shoots bear as a rule both kinds of sexual organs ; such 

 a shoot is always for a long time purely vegetative, and then for a while forms 

 antheridia, and finally a group of archegonia ; sometimes but less often it recurs to the 

 vegetative state after producing antheridia. The antheridia in Radula stand singly in 

 the leaf-axils, and are entirely inclosed in the hollow formed by the great concavity of 

 the lower lobe of the leaf ; they arise from a club-shaped protuberance in a cell of the 

 rind of the stem at the base and in front of the leaf. The group of archegonia in 

 Radida is always at the extremity of the main shoot or of a lateral one, and consists of 

 from three to ten archegonia in a perigynium, which is itself enveloped by two leaves. 

 The archegonia and perigynium are both developed from the apical cell of the shoot 

 and from its three latest segments. The archegonia are formed from the apical cell 

 itself and the acroscopic portions of the lateral segments, the basiscopic portions and the 

 ventral segment being applied to the formation of the perigynium ; their further 

 development has been already described. 



The branching of the thalloid forms was briefly noticed above ; that of the foliose 



ar 



FIG. 104. "jfungermannia bicuspidata. Longitudinal 

 section of the immature sporogonium sg, surrounded by the 

 calyptra ar ; ar' archegonia in which no fertilisation has 

 been effected, / base of the perigynium, st stem, b leaf. 

 After Hofmeister. 



FiO. 103. Diagrammatic representation of the 

 branching of Jungermannieae, the lateral shoots of 

 which appear in place of the under lobe of the 

 upper leaves, apex of the stem seen from above. 

 After Leitgeb. 



Jungermannieae is very varied. These plants have without exception a three-sided 

 pyramidal apical cell, one surface of which is turned to the substratum. The apical cell 

 forms three rows of segments, two of which are dorsal and lateral,' while the third forms 

 the ventral side of the stem. In the species with two rows of leaves a leaf is produced 

 by each segment of the latero-dorsal rows, in those with three rows of leaves each 

 ventral segment also produces a leaf, which is however smaller and simpler in structure, 

 and is known as an amphigastrium. The insertion of the lateral leaves in the mature 

 state is oblique to the axis of the stem, and of such a kind that the lines of insertion 

 of each pair of leaves form a V-shaped angle. This is however the result of displace- 

 ment ; the median planes of the lateral leaves next the apex of the axis are perpendicular 

 to the surface of the stem, and their insertions in accordance with the position of the 

 lateral segments are transverse. Before a lateral segment grows out into a papilla to 

 form a leaf, it divides by a longitudinal wall into an upper, the dorsal half, and a lower, 

 the ventral half, and each of them then puts out a leaf-papilla ; hence it arises that the 

 leaves of the Jungermannieae are to a certain extent halved or two-lobed ; this is usually 



