244 THE AMERICAN MONTHLY [Sept., 



gradually become faintly greenish in the centre, remaining 

 white on the borders of the growing patches. As the days go 

 by the patches increase and thus grow toward each other finally 

 fusing at their edges and making one continuous layer. The 

 conidia are thus seen to be the agents of dispersal. The spores 

 can be sown in a cell in Pasteur's fluid, and the development 

 watched from day to day. 



This is by a process of budding as in the yeast cell. On the 

 surface of the spore a small swelling arises (Fig. 9). This en- 

 larges, it still increases becoming a thread, it is a young hypha. 

 This, besides elongating, soon gives rise to lateral buds and they 

 elongate and in their turn give rise to new hyphtc. The plant 

 thus increases rapidly, each hypha becoming the fruitful parent 

 of many equally fruitful daughters. As to the rate of the growth, 

 this can be observed if you will select some very young bud in 

 a rapidly growing plant and keep it under continuous obser- 

 vation for an hour or so. A series of drawings should be made 

 at intervals of every five minutes to show the diff'erent stag* s 

 of growth. 



The growing hypha? of Penicillium are very interesting for de- 

 tailed and minute microscopic study. They require to be ex- 

 amined with a power of at least 400 diameters to show the 

 points now to be mentioned. They are bounded by a cell-wall 

 which is composed of a peculiar variety of cellulose. Within this 

 wall can be seen the finely granulir protoplasm. In the tips of 

 the hypha? the cell-wall is filled principally with the protoplasm, 

 but in the older parts of the hypha the protoplasm is interrupted 

 with many "vacuoles." These are spaces in the protoplasm 

 filled with water and probably substances in solution. As the 

 most active growth is at the periphery of the circle of the hypha?, 

 these being the younger portions, and as the vacuoles are not so 

 numerous in them we may perhaps conclude that the vacuoles 

 area device for helping to make bulk without using such an ex- 

 pensive material as protoplasm. This is also the case in the 

 higher plants in which we see the cell often very strongly vacuo- 

 lated. 



The hypha? have several modes of branching. Perhai)s the 

 commonest is by lateral buds (Fig. 7), which rapidly enlarge 

 and in their turn produce lateral buds. In other eases the hypha 

 forks so that you cannot say that either branch is the principal 



