MARCHAXTIA POLYMORPHA. 77 



Section or crush a young archegonial hc-.iJ. not exceed- 

 ing a pinhead in size, and giving attention only to the 

 archegonia, notice 

 a. The single layer of cells forming the wall of the 



bulbous part, passing into 

 It. The few rows of cells forming the neck, appearing 



in optical section like two rows, ending above in 



c. The stigmatic cells, which are spread apart at the 

 time of fertilization. 



d. The well denned carify in the bulbous part, con- 

 taining (if not yet fertilized) 



e. The globular oosphere. 



/. The narrow canal extending the length of the 

 neck, through which the antherozoids reach the 

 oosphere to fertilize it. 



ANNOTATIONS. 



In a morphological point of view Marchantia is a 

 plant of unusual interest, on account of its remarkable 

 degree of differentiation. Taking first the vegetative 

 portion, we have in the thallus a structure that is 

 typically shown in lichens and other plants belonging 

 to the thallophytes. More strictly speaking the Mar- 

 chantia stem is only thalloid, for there are the rudi- 

 ments of leaves on its underside, while a true thallus 

 has no leaves. The prostrate position of the stem has 

 necessitated the specialization of the upper surface for 

 the purposes of assimilation and respiration, and the 

 lower surface for the absorption of moisture and the 

 other nourishment which comes with it. 



The chlorophyll bodies, like those of all higher plants, 



