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Mr. B. T. P. Barker. 



formation for the Saceharomycetes. The gypsum-block method gives 

 a plentiful supply, while spore-containing cells are frequently found in 

 old cultures on nutrient media, whether solid or liquid. The spore- 

 containing cells differ from those of most other Saceharomycetes in 

 being compound cells, i.e., they consist of two ordinary ovoid or round 

 cells which have conjugated by means of a beak developed from each, 

 the tips of the beaks fusing, the process thus resembling the well-known 

 case of conjugation of many Algse and Fungi. The compound cells 

 are thus made up of two ordinary yeast-like cells joined together by a 

 narrow neck, the length of which varies according to the circumstances 

 under which spore formation has taken place. 



Details of the process have been observed in hanging-drops of distilled 

 water, in which have been placed a number of vigorously growing cells, 

 the temperature being kept about 25° C. The cells, originally clear 

 and homogeneous, in a few hours began to grow vacuolated, and 

 numerous bright-looking granules made their appearance. In twelve 

 or more hours after sowing, a beak-like tubular process was put forth 

 by many of the cells. The beaks of two neighbouring cells grew 

 towards each other until their tips were in contact. Fusion of the 

 walls then took place at the point of contact, being followed by the 

 fusion of the protoplasmic contents of the beaks, which were clearer 

 and brighter than the rest of the protoplasm in the cells. In a few 

 hours after fusion, the protoplasm began to contract in the cells, and 

 small round masses were formed : these eventually developed into the 

 spores. 



The bright granules in the cells arranged themselves into groups in 

 connection with the above masses and formed a network around them, 

 the final differentiation of the spores being completed by the formation 

 of a cell-wall around each mass. The size of the ripe spore is 4 — 5 /a ; 

 and the number in each compartment of the mature cell varies from 

 one to four, the most common arrangement being two in each. 



The spores germinate in a normal manner. After swelling they bud 

 like ordinary yeast-cells. Fusion of spores in some cases seems to 

 occur before germination. The optimum temperature for spore forma- 

 tion lies between 25° C. and 30° C, the first signs of spores appearing 

 in 16 — 24 hours. At 34° C, 32—36 hours are required, and at 

 36 — 37 C., 2 — 3 days. Above 38° C. no spores are formed. At 

 13 — 15° C., 10—14 days are required, and below 13° C. practically no 

 spores are produced. 



When heated for 10 minutes in beer-wort the spores are generally 

 killed at 60° C, but some withstand an exposure of 5 minutes to a 

 temperature of 65° C. 



In old cultures on nutrient media, and in spore cultures where the 

 conditions were not of the most favourable character for the formation 

 of spores, many cells of exceedingly irregular shape are found. These 



