xoTE t)N poi.ypoKL's n'ciius LE^■ss. 515 



riate 14/'. Sporophorcs on trunk of livinj^ willow tree. 



Plate I5(/. Sporoj)ht)res on roots of livinj^ willow tree. 



Plate 15/). S])orophores at base of dead .-Icacia tree. 



i^ate 15(". SjKirophore which l)roke thr<jngh a concrete floor. 

 and was evidently jj^rowin<^ on a decaying stuni]). Xote 

 the indication of the sei)arate j^ilei and the i^resence of a 

 secondary pileus on one of them. 



Plate 16a. Young sporoi)hore on a dead stump. 



Plate 16b. i-^iseased wood of willow attacked by this fungus. 



Plate i6c. Diseased wood of acacia attacked by this fungus. 



Fig. I (X 300). Spores of the fungus. 



b'ig. 2 ( X 300). Mycelium in wood ]jrosenchyma and medul- 

 lary rays of willow. 



^^S- 3 (X300). Section through laccate cuticle to show the 

 thick-walled palisade layer. 



Fig. 4 (X300). Mycelium of the fungus from willow. 



F'S- 5 (X300). Mycelium of the fungus in medullary ray 

 cells of willow. Note the hyphc-e passing through the pits. 



F'S- 6 (X50O)- Wood prosenchyma of willow showing the 

 delignification and the digestion of the cellulose. Note the 

 cellulose plates projecting into the lumina of the cells. 



Ground Rainbows. — The United States Department 

 of Agriculture Montlily Weather Review, 44 [9], 508, reprints 

 from Seieiice Abstraets a description of a coloured bow similar 

 to a rainbow, with an intensity erpial to that of a good secondary 

 rainbow, which was seen on the ground of a cricket field. The 

 sun was immediately behind the observer, and the bow appeared 

 on the ground, starting from just in front of the observer's 

 feet, and stretching on either side in a sweeping curve away 

 from the sun. The bow was pr(A'ed to be a hyperbola by pegging 

 out its outline on the ground. Tt is explained as being due to 

 sunlight refracted twice. at the near surfaces, and reflected once 

 at the back surfaces of drops of water that had condensed on 

 gossamer which covered the field. According to this explanation 

 a ground rainbow will form a circle if the sun is in the zenitli, 

 an ellipse if the solar elevation is fnMii 42° to i;o°, a parabola 

 when the elevation is 42°, and a hyperbola if it is less than 42''. 



