130 



until a protonemal thread of two to five cells has been formed. The differ- 

 entiation of an apical cell or group is late and irregular, resulting in un- 

 symmetrical growth. The marginal cells show unvisual growth, produc- 

 ing vai'iously formed outgrowths, sometimes bearing autheridia and oc- 

 casionally producing extra growing regions which may e\'en become inde- 

 pendent proliferations. 



With reference to drought resistance the following facts lune been 

 noted : Allowing a culture to become dry for one or two days in the normal 

 air of the greenhouse seems in no way to injure the plants beyond checlc- 

 ing growth during the dry period. One culture left in dry air with slight 

 additions of water once a week showed nearly all tlu^ prothallia alive and 

 in good condition after a period of three months. The major jiart of the 

 plants of another culture are in good shape and have produced a number 

 of sporoi>hytes although subjected to such irregular moisture conditions 

 for a period of nine months. In a culture receiving only air which had 

 been dried by i>assing through, pure glycerine, most of the prothallia were 

 in good condition after four u'eeks and a few survived such treatment for 

 a period of six weeks. 



In conclusion, the two specially important adaptive features are, the 

 unusual power of promiscuous growth of prothallial cells, and the ability 

 to resist extreme desiccation in intermittent periods. 



