216 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



mark of the presence of an oxydase through which that essentia] 

 excitant — oxygen — may be introduced to the root, and it is one which 

 gardeners should notice. It indicates apparently a critical relation of' 

 the plant to oxygen in conditions of physiological drought, and sug- 

 gests to the gardener, therefore, what is necessary for successful culti- 

 vation. Apart from the question of this character as a signal, we 

 know by experiment that a main element in successful cultivation of 

 peat plants attuned to physiological drought is aeration. 



The generation of gardeners who remember the halcyon days when 

 Cape heaths and Australian hard- wooded plants were dominant in 

 horticulture is now almost gone from us. One has learned from them 

 and read with envy of the wonderful specimen plants that were the 

 glory of the horticulture of the epoch. Why has this class of plants 

 dropped out of the domain of modern horticulture? No doubt many 

 causes have operated, and it would be incorrect to specify any one as 

 the chief one. But I do not suppose that I shall be wrong in saying 

 that the supposed difficulty in their cultivation had a large share in the 

 knocking-out process. Wherein lies the difficulty in cultivation of 

 such peat plants in pots? Primarily physiological drought which 

 compels most particular attention to watering. The plant has difficulty 

 in taking in water — the soil is already compact, and each additional 

 watering tends to make it more compact and drive out the air without 

 materially benefiting the water-intake of the plant. In the absence of 

 air the soil becomes more and more acid, and alike therefore in its 

 water-content and in its air-content the condition of the soil becomes 

 impossible to the plant. The gardener cannot here use lime for the 

 neutralization of the acidity, and he must therefore encourage Nature's 

 own process of combustion to prevent increase of acidity by providing i 

 facilities for the entrance of an ample supply of air. i 



The practical side of the problem was recognized long ago by 

 that fine old gardener William McNab, whose skill in heath-culture 

 is a tradition in the gardening world. Keep the peat open by mixture 

 of rubble — air and drainage are the secrets of this cultivation — that, 

 in brief, was his teaching. I 



I have dealt with the special case of permanent physiological! 

 drought in peat plants because, as I have said, it is so familiar a| 

 phenomenon in gardening. Similar drought from other causes implies 

 only other details. j 



The lesson I wish to impress by my theme is that the recognition! 

 of such a condition as physiological drought is of value to the gardener, j 

 Pointedly let me say, dryness at the roots is not always a matter of 

 dearth of water in the soil surrounding them ; and in correlation there- 

 with the problem of watering must be studied in its influence upon 

 oxygenation of the roots. That means life or death. To re-quote my 

 authority, " Improper watering is responsible for more failures than 

 all other causes taken collectively ' ' in gardening. Why ? It means! 

 suffocation. 



Many years ago— but recently enough to be within the recollection 



