ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 829 



the cystoliths of Urticaceae. Only a single species has as yet been 

 observed, parasitic exclusively on Saprolegnia. 



In all stages of development of all three genera cell-nuclei have 

 been observed. Each zoospore, on escaping, contains a nucleus. No 

 sexual reproduction takes place in any of them. 



Fischer gives the following as the distinguishing characters of the 

 three genera : — 



1. Olpidiopsis. The single spore developes as an individual 

 directly into a sporangium. 



2. Woronina. The single spore becomes enclosed as an individual 

 in a soral chamber ; it then loses its individuality, and transforms 

 the entire contents of the chamber into a soral plasmodium. From 

 each spore is developed a single sorus. 



3. Bozella. The separate spores lose their individuality im- 

 mediately after penetrating the host, and mingle their protoplasm 

 with that of the host. In each division of the filament there is not 

 therefore a plasmodium sprung from an entire spore, but only a part 

 of one ; the plasmodium resulting from a spore fills the entire filament. 

 From each spore proceeds a row of sporangia. 



Olpidiopsis is the simplest form of the group, Bozella occupying 

 the highest position, and the three genera are genetically connected 

 as different stages of development. The life-history may be divided 

 into two periods ; in the vegetative period it is a naked mass of proto- 

 plasm, spontaneously changing its form, a plasmodium ; the repro- 

 ductive period is characterized by the separation of zoospore-producing 

 organs. 



The author considers that these three genera must form a group by 

 themselves distinct from the Chytridiaceae, which are characterized 

 by a more or less developed mycelium and by a process of sexual re- 

 production. 



Diastatic Ferment of Bacteria.* — J. Wortmann considers that the 

 reason why bacteria do not, in the ordinary way, attack starch-grains, 

 is that the starch is usually accompanied by albuminoid and other 

 substances, from which the bacteria obtain their food-materials more 

 readily. In order to determine the power of bacteria to decompose 

 starch, this substance must be presented to them in a state of purity. 

 Experiments in this direction yielded the following results : — 



1. Bacteria have the power of producing in starch-grains, starch- 

 paste, and dissolved starch the same changes as are caused by 

 diastase. 



2. Different kinds of starch are dissolved with different degrees of 

 rapidity by bacteria, as by diastase. 



3. The bacteria exercise this influence on starch only when no 

 other serviceable carbon- compound is available, and when the access 

 of air is not in any way impeded. Thus if only the slightest trace of 

 tartaric acid is present in the fluid, the starch is not attacked ; but 

 when this disappears, the starch at once begins to dissolve. 



4. The action of bacteria on starch is brought about by a ferment 



* Zeitschr. fur physiol. Chimie, vi. p. 287. See Naturforscher, xv. (1882 - ) 

 p. 321. 



Ser. 2.— Vol. II. 3 K 



