270 



METHODS IN PLANT HISTOLOGY 



gelatinous horns can be put into a piece of onion-leaf epidermis, as 

 described on page 228. The material can then be stained whole or im- 

 bedded in paraffin. Stain in iron-alum haematoxylin. If mounting 

 whole, when thick glycerin is reached, mount in glycerin jelly and seal. 

 Fewer basidia are torn out from the teliospores, and fewer basidio- 

 spores are torn off from the basidia than when mounting in Venetian 

 turpentine. However, with extreme care, material can be got into 

 Venetian turpentine, and the mounts are firmer. 



The interesting nuclear conditions in the life-history of a rust which 

 has urediniospores, teliospores, basidiospores, and aeciospores, and 



Fig. 74. — Puccinia graminis: A, uredospores on oats, sho^'ing binucleate mycelium and bi- 

 nucleate uredospores with binucleate stalk cells; c, chloroplasts, and n, nuclei of host cells. B, C, 

 and D, stages in the development of the teleutospore; the two nuclei of the binucleate cells in C 

 fuse to form the uninucleate cells of D. X780. 



also pycniospores in the life-history, are not difficult to demonstrate 

 (Fig. 74). Basidia may be mounted whole. The mycelium from the 

 basidiospore, which (in Puccinia graminis) germinates on the barberry 

 leaf, is uninucleate. The binucleate stage begins in the aecium and 

 continues up to the reduction of chromosomes in the basidium, so that 

 the aeciospores, urediniospores, and young teliospores are binucleate. 

 The two nuclei fuse in the teliospore. Reduction of chromosomes 

 takes place during the two divisions in the basidium, and the uninucle- 

 ate stage begins with the basidiospore. Iron-alum haematoxylin is the 

 best stain for the whole series. 



The fleshy fungi. — For habit study, nothing is equal to fresh mate- 

 rial; for second choice, buy canned "mushrooms" (usually Agaricus 

 campestris) at the grocery; forms not readily available in field or gro- 



