192 HOl'MEISTER, ON 



chum filias-mas and Gymriogramma ccdomelanos the first- 

 mentioned form is more frequent. This form answers to the 

 structure of the archegonia in liverworts and mosses, the 

 other corresponds with that of the archegonia of the 

 Equisetacese, Rhizocarpese, and Lycopodiaceas. Ferns con- 

 stitute the intermediate link between these groups, so far 

 as regards the organization of the female reproductive 

 apparatus. 



During the longitudinal development of the neck of the 

 archegonium it bends backwards from the indentation of 

 the fore edge of the prothallium. The amount of curva- 

 ture varies slightly in the archegonia of the same pro- 

 thallium. The archegonia of prothallia which bear those 

 organs on both sides are bent in the same direction, those 

 of the upper surface being usually more curved than those 

 of the lower surface. The curvature is very considerable 

 in the necks of the archegonia of those prothallia which 

 are not close to the earth, but which (in consequence of 

 their growing in masses) have become diverted obliquely 

 upwards. Thus it would seem that the curvature of the 

 necks of arche;onia affords another instance of negative 

 heliotropismus, i. e., of the turning away of an organ from 

 the rays of light. 



The number of archegonia is far less than that of the 

 antheridia. On normally developed prothallia which con- 

 tain an embryonal rudiment, there are seldom more than 

 eight. The development of the archegonia commences 

 close behind the indentation of the fore edge of the pro- 

 thallium, and progresses from thence both forwards and 

 sideways during the continuance of the growth of the 

 prothallium. 



In some prothallia, when growing under a sufficient 

 exposure to light, the rudimentary cells of the archegonia 

 are always on the under surface of the prothallium. Pro- 

 thallia however of the most different species, when growing- 

 erect in closely packed tufts, or in places where few rays 

 of light penetrate, develope archegonia on both surfaces. 

 On the upper surface, which is usually distinguishable by 

 the paucity or absence of rootlets, the archegonia are 

 usually mixed with antheridia. It is evident that shade is 



