50 VAN TIEGHEM AND LE MONNIER. 



connection ; it is necessary to carefully discriminate cases of 

 epiphytism or parasitism from true polymorphism. 



In order to attain this complete knowledge of any given 

 species derived from the observation of the whole cycle of 

 its development, and to avoid the two kinds of difficulties 

 just mentioned, there is obviously only one method. In 

 principle this is extremely simple ; it is necessary to proceed 

 exactly as in dealing with one of the higher plants. We 

 sow a seed and follow the complete vegetative and re- 

 productive development of the plant which is derived from 

 it until the production of new seeds brings us back to the 

 point from which we started. In the present case we must 

 sow a spore and follow without any interruption, and ex- 

 cluding all extraneous organisms, the vegetative and re- 

 productive evolution of the plants which originate from it 

 until we have exhausted the whole series of reproductive 

 forms which the vegetative system of the plant is capable 

 of originating in the different media in which it may 

 be necessary to study it in order to obtain the whole 

 of them. 



The method which we have followed for carrying out 

 practically this principle so simple in theory — the culture of 

 a single spore — includes two distinct parts, which may be 

 termed respectively ' pan-culture ' and ' cell-culture.' 



In pan-culture the nutritive medium, previously, if neces- 

 sary, freed from extraneous living germs, is placed in saucers or 

 pans of porcelain or some porous material, and enclosed under 

 a bell-jar or covered with a glass plate. The nutriment being 

 abundant, the vegetative system acquires extreme vigour, and 

 the fructification attains its most complete development. 

 Specimens can, therefore, be obtained at regular intervals of 

 time, which enable one to judge of the principal characters 

 of the mycelium and its mode of growth, and to study the 

 different stages of development and the structure and dimen- 

 sions of the different forms of fructification which it bears 

 under the most favorable possible conditions. Tlie pan- 

 culture, in addition to this, supplies us with spores for the 

 cell-culture. 



By cell-culture we mean a method in which a spore taken 

 from an unmixed pan-culture is placed, with all necessary 

 precautions, in a drop of liquid accessible in every part to 

 microscopic observation, and known to be free previously 

 from other spores, and which, being enclosed in a cell, is pre- 

 served from subsequent contamination. Those cell-cultures 

 allow of the continuous observation of the plant during every 

 phase of its development, and they are indispensable for 



