278 DEVELOPMENT OF ANTHOCEROS 



first formed by the germinating spore before the characteristic 

 plant is reproduced. 



1 06. Order c. Anthocerotales or Horned Liverworts. — This 

 small group of three genera is the most interesting of any of the 

 hepatics because it presents features that are suggestive of the 

 algae and also of a relationship with the mosses. The thallus 

 is of a primitive type, often with simple lobings and therefore, 

 suggestive of relationship with the simpler Jungermaniales (Fig. 

 198). A peculiar feature of the order is the occurrence of mucil- 

 age cavities which communicate with the air through small 

 openings on the under side of the thallus. These cavities are 



Fig. 198. One of the Anthocerotales, Anthoceros, bearing four pod-shaped 

 sporophytes, 5. The one on the right, s, has opened at the top and is dis- 

 charging the spores, but elongation and the formation of spores continue 

 below owing to its basal growth. 



always occupied by one of the blue-green algae, Nostoc, which 

 possibly assists the plant in the retention of water owing to their 

 mucilaginous character. Another interesting feature of the order 

 is the occurrence of a single chloroplast in each cell, as in Coleo- 

 chaete and several other genera of the algae. The archegonia 

 and antheridia, while resembling those of the preceding orders, 

 are sunken in the tissues. This arrangement doubtless protected 

 the reproductive organs just as did the involucre and perianth 

 in the preceding groups. * 



