PICKETT: A STUDY OF CHEILANTHES GRACILLIMA 333 
marked differences in development. Archegonial plants are 
nearly symmetrical (Fics. 11, 15), with a well-developed median 
thickening, and may reach an extreme length of 2 mm. An- 
theridial plants are much smaller, very irregular in form, without 
median thickening, usually less than 0.5 mm. in length and some- 
times filamentous (Fics. 9, 10), and may have less than twenty 
cells when the first antheridium appears. So small are the an- 
Fic. 16. Normal prothallium showing resumption of growth over wide 
apical area after period of drought. Fics. 17-20. Sporelings showing 
tendency for proliferation through multiple growing points. 
theridial plants and so irregular in shape that they may be over- 
looked in a casual examination of a soil culture. 
The author has elsewhere discussed at length the extreme 
sensitiveness to changing light intensity shown by other fern 
prothallia.* The young prothallia or sporelings of C. gracillima | 
show much of the same sensitiveness. This is well shown by 
Fics. 11, 12, 13, 14 and 16, in which Fics. 11, 14 and 16 are of 
sporelings grown on Knop’s solution in Petri dishes near the 
laboratory window, and Fics. 12 and 13 those of plants from 
*Some ecological adaptations of certain fern prothallia—Camptosorus 
rhizophyllus Link., Asplenium platyneuron Oakes. Am. Jour. Bot. 1: 477- 
498. pl. 49, 60 +f. 1-19. 1914. 
