CEIL FORMATION. 661 



As growth proceeds, these masses become separated, and 

 the small processes or tubes which connected them are 

 drawn out, as it were, and become thinner and thinner ; 

 so that, for instance, in the formation of stellate tissue, so 

 far from the rays having been shot out by unequal growth 

 from special points of the original cell- wall, they have 

 been continuous from the very first. 



Of the Structure and Formation of the simple Cell Muce- 

 dines. The mucedines, commonly called mildews, are 

 among the simplest living things known, and are therefore 

 well adapted for observation. If the membranous invest- 

 ment of a fully developed spore taken from one of these 

 fungi be ruptured, innumerable minute particles, some not 

 more than l-100,000th of an inch in diameter, are set free : 

 these constitute the living growing matter, in contradis- 

 tinction to the envelope or outer part of the cells. " Ger- 

 minal matter " may always be readily distinguished from 

 formed material by its capability of becoming dyed by an 

 alkaline solution of carmine, while the latter remains 

 perfectly colourless. Directly such a minute living par- 

 ticle comes into contact with air or water, a thin layer 

 upon its outer part becomes changed into a soft, passive, 

 transparent homogeneous substance (cell- wall), exhibiting 

 a membranous character, which protects the matter within. 

 Kutrient matter passes through this into the interior, and 

 there becomes changed into living matter ; so that growth 

 takes place, not by additions to the outside, but by the 

 introduction of new matter into the interior. If pabulum 

 be abundant, and the external conditions (temperature, 

 moisture, &c.) favourable, it readily passes through the 

 thin external membrane, and the living matter rapidly 

 increases. But if the external conditions be unfavourable, 

 less pabulum transudes, and the living matter within dies, 

 layer after layer, until the envelope becomes very much 

 thickened, with a proportionate decrease in the size of the 

 living matter. If all this living matter die, and only 

 formed material remain, no increase can take place ; but if 

 the smallest particle remain alive, any amount of living 

 matter, and afterwards of tissue or formed material, may 

 be produced. The position of the germinal matter in the 

 cell varies with the direction in which the pabulum reaches 



