ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 701 



Classification of Diatoms.* — Prof. C. E. Bessey proposes a scheme 

 of classification of the Diatoruaceae founded on that of Schutt, but dif- 

 fering from it in some minor points. He reckons up 72 genera, arranged 

 in 15 tribes. 



Chlamydomonas and its Effect on Water Supplies.! — Mr. G. C. 

 Whipple records an instance, in Massachusetts, in which large quantities 

 of Chlamydomonas pulvisculus, occurring on the surface of a pond, im- 

 parted to the water a distinct unpleasant and oily taste and odour. 



Fungi. 



Propagation of Fungi.| — Herr G. Klebs closes his account of the 

 various modes of propagation in certain fungi by an elaborate review 

 of the physiology of the different processes, from which the following 

 may be extracted as among the more important conclusions. 



He adopts Sachs 1 ' view that one of the main factors is the action of 

 various substances of the nature of ferments. The actiou of external 

 irritants is classified under three heads, viz.: — (1) Those conditions 

 which, under all circumstances, are essential for the inception of the 

 process of propagation ; to these factors he applies Herbst's term 

 " morphogenous irritants." In Saprolegnia a deficient supply of nu- 

 triment is a morphogenous irritant for the formation of zoospores. 

 (2) Those conditions which, by themselves, cannot induce the formative 

 process, but are the necessary accompaniments of other vital processes ; 

 these he terms special conditions. (3) Those conditions which are con- 

 ducive to propagation as to other vital processes, but which can always 

 be altered, within wide limits, without disadvantage. The most efficient 

 morphogenous irritants are changes in the nutrient material. 



Klebs classifies the spores of Fungi, Myxomycetes, and Bacteria 

 under three heads, viz. : — (1) Kinospores, those which are the result of 

 a comparatively simple process of division (motile zoospores, conids, 

 pycnidospores) ; (2) Paulospores, those thick-walled resting cells which 

 are formed by a simple process of transformation of cells or nucleated 

 parts of cells, and serve for perpetuation in unfavourable vital conditions 

 (resting-cells of the MucorineaB, Saprolegniese, cysts of the Myxomy- 

 cetes) ; (3) Garpospores. These, which are the product of a more com- 

 plicated formative process, often formed in special receptacles (zygotes 

 of the Mucorinefe, spores of the receptacles of the Ustilagineae and 

 Basidiomycetes, ascospores, &c). 



The relations between growth and propagation are treated under 

 four heads, viz. : — (1) Growth and propagation are vital processes 

 which, in all organisms, depend on different conditions ; in the lower 

 organisms it is especially external conditions that determine whether 

 growth or propagation shall take place. (2) So long as the conditions 

 favourable for the growth of the lower organisms are present, propaga- 

 tion does not take place. Conditions favourable for this process are 

 always more or less unfavourable for growth. (3) Growth and propaga- 

 tion are also distinguished by the fact that the limits of the general 



* Trans. Amer. Micr. Soc, xxi. (1900) pp. 61-85 (1 pi.). 



t Tom. cit., pp. 97-102 (1 pi.). 



% Pringsheim's Jahrb. f. wiss. Bot., xxxv. (1900) pp. 80-103. 



Dec. 19th, 1900 3 B 



