FUN ARIA HYGROMETRICA 105 



the venter of the archegonium, the stalk, and a part of 

 i he adjacent tissues of the axis to grow so as to form a 

 sheath around the developing sporophyte. But the sporo- 

 phyte soon outgrows this envelope and elongates to such 

 an extent that it breaks it near the base. As the sporo- 

 phyte stalk continues to grow, i L s end carries upward 

 this sheath as the calyptra. Meanwhile the lower end 

 of the sporophyte becomes imbedded in the axis of the 

 leafy shoot, from which it absorbs nourishment for the 

 development of the entire sporophyte. Thus the sporo- 

 phyte is parasitic upon the gametophyte. It may do a 

 little in manufacturing food by means of chlorophyll, for 

 it has stomata and can absorb carbon dioxid, but it 

 must get its water and salts from the gametophyte. 



A relatively small amount of tissue is sporogenous, and 

 there exist in the sterile tissues much more effective 

 devices for protecting sporogenous tissues, and for dis- 

 tributing spores, than existed in the liverworts. It is 

 evident that in this entire plant we have quite an advance 

 in the division of labor among the parts of the plant, 

 and a consequent increase in the quality and quantity 

 of work accomplished. 



It will be remembered that in the Alga Coleochate 

 after fertilization of the egg the tissues adjacent to it 

 are stimulated to growth so that they soon enclose the 

 base of the oogonium. In Riccia after fertilization the 

 tissues continue to grow about and nourish the develop- 

 ing sporophyte. About the base of the archegonium of 

 Marchantia there grows after fertilization an extensive 

 sheath that finally completely encloses the fully formed 

 sporophyte. In the mosses, when the fertilized egg has 



