TRANSACTIONS OF SECTION D. 781 



10 Conditions affecting Plant Life in a Toivn Atmosphere. 

 By G. H. BAir,EY, D.Sc, Ph.D. 



Altliougli it is well known that plants in towns exist under very unfavourable 

 conditions, there is very little precise information as to the nature of these 

 conditions. A series of observations extending over more than a year, and carried 

 out by tlie Town Gardening Committee of the Manchester Field Naturalists, in 

 conjunction witli the Royal Horticultural Society, have supplied many important 

 details, a summary of which is given below. 



1. A comparative measure of the amount of light received each day at stations 

 in different parts of Manchester and district and in other localities shows that, 

 whilst tl>e record for the suburbs of a large town falls below that of a country 

 district, there is a still greater falling off to the extent of 50 per cent., or even more, 

 within the town area. For the same period of the year the measure for bright 

 sunshine is ten to twenty times that for dull weather, and as much as 300 times 

 that during dense fog. As to the effect of the season, an hour's sunshine at 

 midday in June gives five times the record of that for December. 



Moreover, comparative measures for sunshine taken simultaneously in Switzer- 

 land, Torquay, and the suburbs of Manchester were in the proportion 20 ; 11 : 3. 



2. The amount of sulphurous acid in town air in heavy weather is ten to 

 twenty times that in bright clear weather, and in fog the proportion is still greater. 



3. Freshly fallen rain collected in Manchester showed as much as seventy 

 parts per million of sulphuric acid. 



Snow is usually more free from sulphuric acid than rain, whilst rime, which 

 has formed on the leaves during frost, is by far the most impure form of moisture 

 which comes in contact with plants, and samples have been collected containing 

 nearly 400 parts per million of sulphuric acid. Estimations have also been made 

 of the amount of organic matter and soot deposited on the leaves of plants, and 

 the nature of the deposit has been examined. 



11. Some Alhucas and their Eyhrids. By John H. Wilson, B.Sc, F.R.S.E. 



The African liliaceous genus, Albuca, is easily recognised by the cucuUate and 

 connivent inner segments of the perianth, which commonly conceal the essential 

 organs as in a capsule. The writer confined his remarks to the following 

 species : — A. con/mbosa, A. fastigiatn, A. caudata, A. juncifolia, A. trichophylla, 

 A. major (?), and an unidentified species. 



During the past six years a number of hybrids have been raised by the writer. 



Using the initial letter as an abbreviation of the specific name, and placing the 

 seed-bearing parent before the sign of hybridity, the following is the series involv- 

 ing A. fastigiatn and A. conj)Hbosa:—f.<c, (fxc)xc, ( /xc xc)xp, (fxc)x 

 {fj^exc),{.f>^c)^f,cy.{fxc),cx{fxcxc). 



The following involve A. trichophylla, A. juncifolia, and A. major : — t x c, 

 t^ft>:{fxc),fxc)xj,fxj,ifxc)xm. _ ^, ^.j , . , 



During the present summer capsules of a series of hybrids having A. caudata 

 {ca) as one of the parents has been secured, viz.:— caxc, cax{fxc), fxca, 

 {fxc)x ca. 



Two capsules were also borne by the unidentified species, resulting in the one 

 case from double poUination by tx{fxc), and m; and in the other by c, and 

 / X (/x c). It will be instructive to see, by study of the hybrids furnished by 

 these experiments, which pollen of the three kinds applied has been eftective. 



A brief description of the prominent features of the hybrids of previous years 

 was given, reference being especially made to the bulbs which, no less than the 

 flowers and foliage, aftbid many points of interest. The characters of certain of 

 them have already been discussed ('Botanisch Jaarboek,' vol. iii. 1891, p. i>33). 



Hybrids between species having in the one parent erect, and in the other 

 cernuous flowers, are txc, tx{fxc), and {fxc)xj. The characters of both 

 parents are fairly equally blended iu the first two. The flowers during the day 



