xv ASEXUAL REPRODUCTION 161 



So that the mould consists of an interlacement of branched 

 cylindrical filaments, each consisting of a granular substance 

 completely covered by a kind of thin skin of some clear 

 transparent material. 



By the employment of the usual reagents, it can be ascer- 

 tained that the granular substance is protoplasm, and the 

 surrounding membrane cellulose. The protoplasm moreover 

 contains vacnoles at irregular intervals and numerous small 

 nuclei. 



Thus a hypha of Mucor consists of precisely the same 

 constituents as a yeast-cell protoplasm, containing nuclei 

 and vacuoles, surrounded by cellulose. Imagine a yeast 

 cell to be pulled out as one might pull out a sphere of clay 

 or putty until it assumed the form of a long narrow cylin- 

 der, and suppose it also to be pulled out laterally at intervals 

 so as to form branches : there would be produced by such a 

 process a very good imitation of a hypha of Mucor. We 

 may therefore look upon a hypha as an elongated and 

 branched cell, so that Mucor is, like Opalina, a multinucleate 

 but unicellular organism. We shall see directly however 

 that this is strictly true of the mould only in its young state. 



As stated above, the aerial hyphse are at first of even 

 calibre, but gradually swell at their ends, forming sporangia. 

 Under the microscope the distal end of an aerial hypha is 

 found to dilate (Fig. 36, c 1 ) : immediately below the dilata- 

 tion the protoplasm divides at right angles to the long axis 

 of the hypha, the protoplasm in the dilated portion thus 

 becoming separated from the rest. Between the two a 

 cellulose partition or septum (sep) is formed, as in the ordi- 

 nary division of a plant cell (Fig. n, p. 66). The portion 

 thus separated is the rudiment of a sporangium. 



Let us consider precisely what this process implies. Before 

 it takes place the protoplasm is continuous throughout the 



M 



