Ch. XI] 



THE LIVERWORTS 



483 



ing two horizontal ranks of very delicate 

 leaves (Fig. 341). These are scale-like, 

 one cell-layer thick, without midrib, and 

 very pleasing to see under the microscope. 

 In some epiphytic forms the lower lobes 

 of these leaves are developed to water- 

 holding sacs ; and many kinds have also 

 a third row of smaller 

 leaves along the under 

 side of the stem. The 

 antheridia occur among 

 the leaves on side 



Fig. 342. — Antho- 

 ceros Icevis, natural 

 size. 



The walls of the 

 vertical sporogonium 

 split in two valves 



branches, but the arche- from the columella, 

 gonia mostly terminate ^^^ 

 the main shoots. The 

 sporogonium develops an elongated stalk 

 and opens by four valves. Vegetative 

 reproduction also occurs through various 

 special bodies. 



Order 4- Anthocerotales : the An- 

 thoceros and kin. These inconspicuous 

 Li vei worts form a small order, but are 

 highly interesting because their structure 

 suggests a possible mode of transition be- 

 tween Bryophytes and Pteridophytes. The 

 thallus is simple, and rests on the ground 

 like a Riccia (Fig. 342) ; but the 

 archegonia and antheridia are sunken 

 in the upper surface. The striking 

 feature is the sporogonium (Fig. 

 343), which differs from that of 

 SL'rfLttlK other Liverworts in several respects. 



KOIllUIll 



median vertical lection, It has a very slender elongated 



SEZTSbrtSrS f °™> and 8™™ continuously from 

 ■haded: the base; the spores are borne not 



