130 DIMORPHISM IN FUNGI, 



Structure in different specimens, especially the mycelium, and the 

 frequent sources of error that arise in the course of experiments 

 from the universal dispersion of spores of all kinds in the atmo- 

 sphere, and from the undoubted hereditary fungoid infection in 

 many plants. 



For the sake of clearness, we can divide our subject into two 

 groups : — 



I. — That in which two or more forms occur consecutively or 

 simultaneously on the same individual. 



2. — That in which two or more forms appear on a different 

 mycelium, on a different part of the same plant, or on a matrix 

 wholly distinct and different. 



The examples to be brought forward are simply illustrative and 

 suggestive. It would be impossible, within the limits of an ordi- 

 nary paper, to deal exhaustively with the subject. 



Taking, then, the first and simplest division, we have a 

 common example in the well-known mould, Aspergillus glancus, a 

 specimen of which would be furnished from almost any house- 

 keeper's jam-cupboard. 



From the superficial threads of the mycelium arises a straight 

 tube, which swells at the end, and becomes covered with numer- 

 ous protuberances. Each of these protuberances becomes con- 

 stricted just below its termination, and gives rise to a small cell 

 filled with protoplasm. After a time a second cell is produced in 

 the same manner, which pushes the first before it, and so on until 

 a chain of spores is formed, those at the end being the oldest. 

 These are the conidia, which drop off as they become ripe, and 

 are capable of reproducing their kind. 



But from this same mycelium, when it gets older, very small 

 branches are thrown out, which terminate in a spiral manner. 

 These small terminal spirals enlarge laterally, and a complicated 

 change takes place, resulting in the formation of a globose recep- 

 tacle of thin, delicate cells, containing a closely-entwined mass of 

 cells. The whole mass enlarges in size. The outer wall becomes 

 compact and of a yellow colour, and the contained mass of cells 

 becomes converted into a mass of spore-cases or asci, each of 

 which contains eight spores. When ripe, the walls of the concep- 

 tacle become brittle and give way, and the spores are liberated. 



