ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 93 



aid of his theory, and explains the phenomena on which he based it ; 

 chiefly appealing to the different electrical polarities of the substances 

 employed — a line of argument familiar to most of those who have 

 studied the question of the origin of life. 



It is to be observed, in estimating the scientific value of these 

 experiments, that the highest magnifying power mentioned as being 

 employed is 610 diameters, and that as a rule no special attention 

 appears to be given to the cleaning of the vessels, or the sterilizing 

 of the air or water, the latter being as often ordinary sprint- or 

 stream-water as distilled. The value of the reasoning is still further 

 impaired by the fact that the latest experiments which have been 

 adduced in opposition to the ancient theory here advocated afresh are 

 dismissed without much consideration, even those of Tyndall receiving 

 but scanty attention. 



Prolongation of Vegetative Activity of Chlorophyllian Cells 

 under the influence of a parasite.* — According to the Schwendenerian 

 theory lichens are complex organisms, consisting of an alga, and a 

 fungus which is parasitic on it. It seems extraordinary that the alga, 

 thus embraced by a parasite, not only continues to live, but increases 

 and multij)lies, and is apparently endowed with new vigour. The 

 same alga, alone, becomes discoloured and disappears on the return of 

 the dry season ; but in the lichen state it often persists for years. It 

 has been said by Kees, that there are no other such cases known of 

 vegetative activity being prolonged under the influence of a parasite ; 

 but Max Cornu has lately called attention to several. Thus, maples 

 are often attacked, late in summer, by an Erysiphus which occupies 

 the under surface of the leaves. The parts thus occupied remain 

 green when the rest of the leaf has withered, and even after the leaf 

 has fallen. Similarly with a parasite which attacks leaves and fruits 

 of pears, apples, &c. ; indeed, the fact is very general ; the chlorophyll- 

 cells attacked retain their green and their vital activity longer than 

 the others. The phenomenon is explained by the fungus counter- 

 balancing the return of nutritive matters towards the reserve centres. 

 Green algae have a vegetative period, during which they retain this 

 colour very intensely ; then they grow yellow and form durable 

 spores, after which the vegetative part dies. In lichens the fungus 

 prevents this development of spores, and so favours the life of the 

 alga. Flowering annuals similarly may be preserved many years by 

 prevention of flowering. 



Algae. 



Classification of Nostoc. — In the second fasciculus of MM. 

 Bornet and Thuret's ' Notes algologiques,' M. Bornet gives a full life- 

 history of the genus Nostoc, including the germination of the spores 

 and the development of the hormogonia, which display motility after 

 their escape. The thickening of the filaments takes place in many 

 species, without having any specific value. With Nostoc M. Bornet 



* Comptes Rendua, xciii. (1881). See also Mr. P. Geddes' recent researches 

 on " Animal Lichens," ' Nature,' xxv. (1882) pp. 303-5. 



