THE MARSILIACE^E. 189 



these are separated by many transverse divisions, each 

 containing a sorus. Around the inner wall of the sporo- 

 carp runs a gelatinous ring to which the sori are attached, 

 and, when the sporocarp opens, this ring absorbs water and 

 increases enormously in size, by this means pushing out 

 of the sporocarp and drawing the sori with it. The 

 whole process may be completed in half a day, and may 

 be witnessed by any who will take the trouble to soak a 

 Marsilia sporocarp in waten Before soaking, a small 

 part of the outer covering of the sporo- 

 carp should be chipped off, so that the 

 water may enter. The small oblong sori, 

 attached to the almost transparent ring 

 of jelly, make it a most interesting object. 



A 1 1 e -11 r i i Cross-section of 



An illustration of it will be found at the Piiuiaria sporocar 



, . . f ^ . , ~ , (Enlarged.) 



beginning of this chapter. Each sorus 

 contains both megasporangia and microsporangia, the 

 former few in number and each containing a single ivory- 

 white megaspore. The sporocarps have a very thick, 

 hard wall almost impervious to water, and may remain 

 beneath the water for a long time without opening. So 

 nearly impervious to liquids are the sporocarps when 

 uninjured, that they have been kept in 95$ alcohol for 

 nearly six years, and then the spores still had vitality 

 enough to germinate. Sporocarps dried and kept in the 

 herbarium for eighteen years have also produced spores 

 capable of growing. 



The sporocarps of Marsilia finally open by splitting 

 into halves. Those of Pilularia split into four valves 

 from the apex. Since the sporocarps are modified leaves, 

 the four valves of the .Pilularia sporocarp may be taken 

 to indicate that the original leaf was like that of Marsilia. 

 Baker therefore states that the leaf in Pilularia is now 



