132 Practical Plant Biology. 



the stalk and the foot, the archegonium is stretched and keeps 

 pace with the growth of the embryo within. Outside the arche- 

 gonium a collar of tissue grows up round it and arches over it 

 and finally the stalk of the archegoniophore elongates consider- 

 ably, so that it becomes 3 or 4 cm. long. Evidently the effects 

 of fertilisation are not limited to the ovum but they are transmitted 

 to the surrounding tissues. 



When the spores and elaters are ripe within the capsule, or 

 sporangium, the stalk elongates and shoves the sporangium out 

 through the top of the archegonium, and out of the in-arching 

 collar, so that it hangs down free and uncovered from the under- 

 side of the archegoniophore. At first the protruding sporangium 

 looks like a dark green knob. Later it becomes yellow in colour 

 and splits at the top with 4-6 radial clefts. The mass of spores 

 and elaters, which were apparently in a state of compression, 



FIG. 25. Marchantia polymorpha, top of archegoniophore, vertical section, 

 x 8. Fertilised archegonia with embryo-sporophytes in different stages 

 of development are seen. 



expands and a large number of spores are liberated. The re- 

 mainder are retained in the tangled mass of elaters, which adheres 

 to the base of the sporangium, and are shed out in dribs and 

 drabs by the hygroscopic curling and uncurlirlg of the elaters. 

 These motions of the elaters are due to the unequal expansion 

 of the cellulose wall and of the spiral bands of the elaters when 

 imbibed with water. Hence motion must result, when they lose 

 water to a dry, or absorb water from a moist atmosphere. The 

 whole apparatus acts like an intermittent censer or pepper-pot, 

 shaking out small quantities of spores at a time. The height of 

 the archegoniophore facilitates this scattering, so that the spores 

 will not fall out on the soil in a compact mass. 



Thus we find an advantage in the elevation of the archegonia 

 in the archegoniophore which compensates for the difficulty that 

 elevation introduces in the way of fertilisation. The spores on 

 reaching the ground germinate immediately and produce a small 



