100 



the Alps the lank Spjiegina ditnipes before Saxifraga rotundifolia 



and in my garden Ascia podagrica before Saxifraga uinbrosa. 



Of Verbascum nigrum the main fertilizers are humble-bees, Dip- 



tera co-ope'rating only in a subordinate degree; in the case of the 



three other species, on the contrary, the above-named Syrphidae are 



such frequent visitors and cross-fertilizers that we may safely conclude 



that it is by their selection of elegantly-colored varieties that these 



flowers have acquired their beautiful^ peculiarity. Hence, in order 



to estimate the color-sense of these Syrphidae, it is worth while to 



consider what color-combinations they have been able to produce 

 by their selection. 



Saxifraga umbrosa being, as far as hitherto known, their finest 

 masterpiece, we may in the first place look at the variegated decora- 

 tion of this species. Its snow-white petals are adorned with colored 

 spots, which in size and intensity of light gradually decrease from 

 the base of the petals towards their extremity. Indeed, nearest to 

 their base, within the first third of their length, there is a large irreg- 

 ular spot of an intense yellow ; about the middle of their length there 

 follows a narrower cross band of red color, vermilion towards the 

 base, intensely pink towards the outside, not reaching the margins of 

 the petals, sometimes dissolved into several separate spots ; lastly, 

 beyond the middle of the length of the petals there are three to eight 

 smaller roundish spots of a paler violet-pink color. 



The flowers^ of Veronica chamaedrys prove that also gay blue 

 colors are perceived and^ selected by Ascia. 



On some Impurities of Drinking- Water. — Under this title. Prof. 

 W. G. Farlow has recently sent us a pamphlet recording the results 

 of his investigations, extending over several years, as to the causes 

 of the '' pig-pen " odor which occasionally makes its appearance in 

 water stored up for the use of cities. The subject is discussed in a 

 popular form, and from strictly a botanical point of view. Prof. 

 Farlow has traced the cause of the odor in question to the putrefac- 

 tion of algae belonging to the order Fhycochromaceae. This order 

 contains certain genera, three at least of which have been found in 

 decay to cause disagreeable conditions of drinking-water - 'these 

 genera being Clathrocystis, Caelosphaerium and Anabaena, So' far as 

 known, the so-called " cucumber taste," which also sometimes makes 

 its appearance in drinking-water, is not due to the growth or decay 

 of any species of plant; nor can any cause— botanical, zoological, 

 or chemical be assigned for it. A perusal of Prof. Farlow's paper 

 will serve to allay the fear of those who see in every minute alga 

 floating in water the germs of disease. 



The August number of the Phrenological four nal, received July 

 20th, contains a portrait of the late Charles C. Frost, accompanied by a 

 biographical sketch from materials furnished by Rev. Lucius Holmes 

 To the American Monthly Microscophical fournal Dr. Wolle con- 

 tributes another note on fresh-water algae ; the subject treated is the 

 %^^M% Bulbochaete, and figures of six species illustrate the text. 



§ 8l. Erratum —In Mr. EIHs's description of a new Sphaeria p go 6 lines 

 from the bottom of the page, strike out the comma after the word *' J;>mV/d 

 Although Mr. Ellis's communication is dated May 26th, it was not received bv 

 till the latter part of July. ^ 



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