214 JOUENAL OF THE EOYAL HORTICULTURAL SOCIETY. 



hairs, but in the Melastoinaceae the root-hairs develop and spread out 

 through the mucilage. 



These two features — the mycorrhizal fungus and the mucilage — in 

 the roots of peat plants, whilst related, as I have suggested, to 

 physiological drought, and to be interpreted partly in terms of it, 

 have otherwise a significance in horticulture for a notice of which I 

 wish to find a place here. 



There is no cultural fact in gardening that obtains more recogni- 

 tion than this : lime in the soil is hurtful to Ehododendrons and other 

 peat plants. You cannot grow Ehododendrons in a hme soil; if 

 you wish to grow them in such conditions, you must dig out pockets 

 for peat in which to plant. All of you have heard these statements, 

 and will probably be inclined to agree with them. I have not yet 



Fig. 71. — Eoot-tips showing Mucilage Sheath. In the Figure on Left the 

 Bed Oxidation Tip shows clearly as a Dark Spot within the Mucilage. 



found, in cases where I have learned the Ehododendrons were growing 

 in a lime soil, that they had not been planted otherwise than I have 

 stated. Even watering with hard water has a harmful effect. 



Y/hat is the cause of this? These plants are attuned to acid soil, 

 and the suggestion is open that this acidity may be in some measure 

 neutralized by the lime, and the amount so modified as to make the 

 normal adaptation unworkable. Possibly, if the lime enter. But I do 

 not think the cause rests in this single soil factor if it operate. There 

 is evidence pointing to a direct influence on the plant itself through 

 the two root features I have already referred to — the fungus of the, 

 mycorrhiza and the mucilage secretion— and these are, I suggest, byj 

 far the most important elements in the case, and on the following,' 

 grounds : — 



Although direct experiments are yet wanting, so far as I know 



