IP o 5 te isia 



ready a condition of long standing. Is 

 there any reason to suppose that 

 this retention of the gametophyte has 

 caused the embryo sporophyte to dis- 

 card the ancestral nursing organ, the 

 nursing-foot, and employ in its place 

 foliage-leaves, structures characteristic 

 of the free life of the sporophyte ? 



From this point of view a cotyle- 

 donary structure first makes its 

 appearance in the He pa tics. The 

 sporophyte of Riccia absorbs nourish- 

 ment throughout its entire surface, but 

 that of Marchantia responds to its 

 parasitic condition by the sterilization 

 and specialization of a portion of its 

 tissue as an absorptive organ, com- 

 monly termed the nursing-foot. In 

 Marchantia the nursing-foot consists en- 

 tirely of tissue derived from the hypo- 

 basal cell of the segmenting oosperm, 

 but in Anthoceros and the Jungerman- 



