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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



of the appearances exhibited in a large number of cases of injury 

 would be rather premature. 



To sum up the effects produced in floral organs. There is 



(1 ) Plasmolysis and consequent collapse and translucency 

 of the tissues. 



(2) A loss of colour or bleaching. 



(3) A yellowing, due to oil and to a generally diffused 

 yellow coloration. 



(4) A browning, due to a fine precipitate in the proto- 

 plasm. 



Sometimes (3) and (4) are not readily distinguishable, or they 

 may both be present, as may (2) and (4). The plasmolysis (1) 

 is invariably present. 



In discussing these four classes of change, I regard whatever 

 is said as tentative. I have not yet sufficiently probed this 

 department of injury. 



(1) The plasmolysis and accompanying changes I regard 

 as due to the direct action on the living cells of poisonous 

 vapours in the air. It is the same phenomenon as has been 

 described (p. 28) for foliage, though, from the extreme delicacy 

 of the tissues of the floral organs, its effects are here accentuated. 

 Any poisonous vapour would have this primary effect ; be it 

 sulphurous acid, ammonia, or one of the volatile oils. 



(2) The bleaching is not inconsistent with the action of 

 sulphurous acid. This vapour, I apprehend, attacks the tissues 

 direct. Instances often occur in which the drippings from the 

 condensed moisture on the glass fall on to the flowers, bleaching 

 the corolla locally. This is frequent in pink varieties of Bou- 

 vardia. Identical with this is Prof. A. H. Church's observation* 

 of Convolvulus major, growing in the Portland Eoad, with flowers 

 bleached by rain-drops. That a corrosive action of sulphuric 

 acid, similar to that described in Section I., A, occurs in the case 

 of flowers, I have been unable to determine. It is with some- 

 thing more rapid that we have to deal here. Still, such action 

 may be one co-operating cause in the injuries. 



(8) The characteristic yellowing which sometimes occurs is 

 difficult to trace. Sulphurous acid alone cannot account for 

 its appearance. Of the many vapours which I have applied, 

 * Journ. Roy. Hort. Sue. vol. xi. p. lviii. 



