238 Salisbury . — The Extra-floral Nectaries of the 
If, however, fresh secretion from another nectary be placed upon the glands 
they function again. 
Washing nectaries with o-i per cent, corrosive sublimate solution 
killed the gland cells, and no further secretion took place. 
The same result obtained when the nectary was washed and the gland 
cells carefully scraped off with a scalpel. 
The root pressure was determined for an actively secreting plant 
of P. cuspidatum , and was found to be equivalent to 13-1 cm. of mercury. 
Water injected at a higher pressure only produced an increased secretion 
or rather bleeding from the lowest nectary of the shoot employed. 
Secretion was equally active where the shoots were removed and 
placed with their cut ends in water. 
Placing plants in saturated or nearly saturated air caused marked 
increase of secretion — this latter appearing as large drops clinging to the 
nectaries. The control plants showed no such increase. It was found that 
where the plants which were placed in saturated air possessed few shoots, 
and therefore few nectaries, the whole of the nectaries showed an increased 
activity. 
But where large plants were used which bore numerous nectaries, only 
a few showed increased secretion. 
One plant which bore fifty-two glands was placed in damp air. When 
examined after three hours only two nectaries were actively secreting. 
The removal of eight leaves was followed after twelve hours by an 
increase in the number of actively secreting nectaries to six. 
The result may have been due to an increase in the saturation, but 
a plant with a large number of nectaries, of which only three were secreting 
vigorously, showed an increase to only five after a lapse of sixty hours. 
Where in the case of plants bearing numerous shoots one or two 
of these were enclosed in saturated air, whilst the remainder were in 
comparatively dry air, no increase of secretion was observed on the nectaries 
of the enclosed shoots. 
Plants, which, in saturated air, had drops of secretion hanging to the 
nectaries, rapidly lost their drops on removal to dry air. In order to 
determine whether the loss of the drops was due to evaporation or absorption 
by the glands, control-drops of water of similar dimensions were placed on 
the axes and petioles. It was found that the drops of secretion were the 
first to disappear, notwithstanding their slower rate of evaporation in con- 
sequence of the dissolved sugar. We appear then to have glands here 
which, like those described by Kerner ( 10 ), are at once secretory and 
absorptive. 
Experiments in saturated air were also performed upon the gum- 
secreting leaf-glands, and these too (particularly those of the ochrea) prove 
to be more active under that condition. 
