48 Mr W. Gardiner, On the Physiological [Nov. 12, 



believe is rather the exception. Again, one cannot agree with the 

 way in which certain of Dr Wilson's experiments were performed. 

 Thus, it does not seem fair to make deductions as to the production 

 of nectar flow, when the osmosis was caused by particles of sugar, 

 which when dissolved, produced a very strong solution of great 

 osmotic activity. We should hardly expect that this would act 

 in the same way as a solution of a normal nectar which in some 

 cases, e. g. Fritillaria, contains only 1 p. c. of sugar. As regards 

 the constitution of nectary cells, one knows that their walls are 

 very thin, and it seems quite possible that by the repeated 

 washing with water a perceptible amount of sugar is removed 

 from the cells, and that some account must be taken of the 

 stimulus caused by the action, and the quantity of the water used 

 in washing. We can, I think, understand that such treatment 

 would be quite capable of seriously interfering with the normal ,.. 

 cell equilibrium. Thus there is reason to believe that while 

 Dr Wilson has made most valuable observations with regard to 

 the secretion of nectar, he has not explained the cause of the 

 secretion in the first instance. W T hat does appear to be of special 

 value is the great probability that the nectar at first secreted 

 may by gradual concentration act by mere osmosis and attract 

 more nectar from the tissue long after the cell is secreting in virtue 

 of its own activity ; and I am led to think that this goes far to 

 explain both his own and Darwin's 1 observations, that the 

 exudation of nectar takes place more rapidly in sunlight, for 

 according to my own observations as regards water-glands and 

 the like it does not seem probable that the power of secretion as 

 such is accelerated by light. 



One must conclude that the secretion of nectar in the first 

 instance can only be explained in the light of Sach's views. We 

 have brought before us again and again so many and so striking 

 examples of the fact that the vegetable cell can so easily take 

 up water on one side and exude it on the other ; a fact which 

 from some points of view might well be regarded as a property 

 par excellence of living vegetable tissue ; a fact moreover which 

 in the end may be explained as the effect of a somewhat complex 

 physical law, but of which we have at present no explanation. 

 Most striking examples of this force are afforded by root- 

 hairs, and by the epidermal cells of such glands as those of 

 Limoniastrum. In fungi, e. g. the unicellular Mucor in Pilo- 

 bolus, in the root-hairs of Marchantia, and finally, as Sach 

 has shown, in pieces of the cut stems of young grasses when placed 

 in damp earth the same phenomena prevail. 



In fact, there can be but little doubt that in nectaries the first 



1 Darwin, Cross and Self-fertilisation of Plants, p. 403. 



