2 THE AMERICAN MONTHLY [Jannaiy, 



cracker some of the dust. Cover each tumbler with paper to keep out 

 dust but to let in air Put them away, a set of three in a moist dark 

 phice, a set of three in a moist light place. In the pure water, whether 

 in the dark or the light place, two or three days will have produced no 

 change. In the svrup or the cake, from both places, spots of green 

 will have appeared upon the surface. Therefore, mould grows in the 

 dark as well as in tlie light, and will not grow in water containing no 

 organic matter. 



In similar ways it may be shown that mould grows well on meat 

 broth and other waterv media ; that it grows faster in warm places and 

 slower in cold places. 



2. Examination with Low Power. — Upon the tip of a needle 

 catch the smallest possible speck of mould, add a drop ot water, cover 

 it and place under the low power. There will perhaps appear some 

 very fine threads, but mainly a great dimness with some very dark 

 curved lines. This mount is a failure, proving that w^ater is not a uni- 

 versal mounting medium. That might have been suspected from the 

 water not moistening the film when first tried. Begin again with the 

 needle, and now use alcohol upon the slide. When viewed under the 

 microscope it will appear that the mould is made up of fibres matted 

 together. These will show still better under the high powers. Before 

 using them, mount a new slide in alcohol, carefully teasing the speck 

 of mould before covering it. To "tease" it. take a needle in each 

 hand, hold down the speck with one needle and pull the mould away 

 with the other one. This separates the fibres for easier inspection. 

 As the alcohol evaporates rapidly meanwdiile, some more must be 

 added from time to time, getting it under the cover with a pipette. 



3. Under High Pow^er. — The teased speck now appears to be a 

 great complex of fine wavy threads. They make up the large part of 

 the mould, and are called Hyp/ice (webs) because of their being matted 

 and woven together. These are of two kinds: — (i) which run indefi- 

 nitelv. many having no cross partitions ;(2) which are broken by trans- 

 verse joints and which terminate in branches tipped with small spheres. 

 Besides these two kinds of hvphae numerous small spheres called conidia 

 will be found in the mount. The hypha and conidia together consti- 

 tute the mould. The next question is, how are they put together.' If 

 a mould growing on a fluid-like broth be carefully examined one can 

 see that it consists of a coat or scum which floats on the fluid, and that 

 from this, called the mycelium, hyphae carrying the dust before noticed 

 are borne aloft into the air. These are invisible to the naked eye, but 

 careful examination of bits caught with the needle from such a film 

 convinces vou that there are two kinds of hyphae. those of the mycelium 

 and others arising from them into the air. 



4. The Mycelial Hyphse. — A single thread from the complex, 

 under medium power, is illustrated in figure i of the plate. Observe 

 the long and narrow, flexuous, and parallel-sided thread or hypha : 

 tliat it branches frequentlv ; that these branches are of equal diameter 

 with the main stem ; that the stem is not empty but contains something, 

 and that the stem is one continuous tube through all its length and not 

 broken bv subdividing cross-walls. The older mycelial hyphie are not 

 one single tube, but, like the aerial hvpha^, arc transxersely divided. 

 In ncAvlv raised nncelium manv of the undi^ ided ones will l>e knnul. 



