178 BOTANICAL GAZETTE [September 



stains. Shrinkage in the young embryo and resistance to infiltra- 

 tion of the mature capsule were the chief difficulties met. 



Thallus 



Schiffner (23) describes Aneura pinguis as a cosmopolitan 

 species, strictly dioecious. Land reports the growth of the species 

 on decayed fallen logs in the rain forest as most luxuriant. The 

 plants exceed only slightly, however, those growing in the hydro- 

 mesophytic habitats of Chicago. On fallen hemlock logs in shady 

 ravines and on the mossy edges of pine-oak dunes bordering sloughs 

 the plants form a close mat. Wherever moss forms a humus layer 

 along the lines of seepage of the clay bluffs along Lake Michigan, 

 the thalli are also found. In the prairie meadows Aneura pinguis 

 often extends half an inch on Typha and Acorus leaves or grows on 

 clumps of exposed grass roots. In all these places moisture, 

 diffused light, and fairly low temperature are the favorable condi- 

 tions for its growth. Plants grow fairly well in the laboratory 

 when these conditions are imitated. 



p 



margins 



In general the thallus is a flat ribbon-shaped plant closely appressed 

 to the ground, with frequent branches, and slight indentations 

 along the margins. While it averages 5-7 mm. in width, it may be 

 reduced when growing in a moist chamber with light from one side 

 in the laboratory to less than 2 mm. (Nemec 21). 



compact 



main axis of the 



mi 



the plant is usually thicker along the center, thinning out toward 



margins 



some 



time and the plastids often have 5 or 6 starch grains. Ordinarily it 

 is 10-12 cells thick. There is no definite differentiation into tissues, 

 but the superficial layer is clearly composed of smaller cells with a 

 larger number of chloroplasts. This dorsal " small-celled epider- 

 mis" has undergone one more division, longitudinally and trans- 

 versely vertical, than the layers beneath (fig. 2). Plants in the 



and are deeu emerald green in color. The 



numerous chloropl 

 or Elodea. 



