LEAF-BLADDERS IN EICHHORNIA SPECIOSA. 221
not produce such a large number of axillary shoots, nor do they exhibit such a pronounced rapidity of growth as is seen in the other plants. The transitional forms are shown in the diagram below.
Physiology : — In order to find out the behaviour of the plant in culture, I had a bladderless plant transferred to a jar containing the necessary salts dissolved in rain water according to Crone's formula. The appearance in a few days of swollen leaf stalks suggested that the chief stimulating factor was water and an examination of both bladdered and bladderless leaves would, it was thought, disclose either some difference in the water content or some sort of constitutional change brought about by the excess or deficiency of water. It is well known that stomata regulate their openings according to the amount of water present in the transpiring organs and thereby prevent too much loss of water from plants. A greater water content will thus keep them open whereas a diminished supply will tend to the closing of the aperture. A highly useful method of ascertaining the width of the stomat.il opening is afforded by the work of Ujin (fi) on the regulation of stomata. This author and Lloyd have shown that simultaneously with the opening of the stomata, the starch present in the guard cells disappears in some way probably by enzymic activity in the presence of a greater quantity of water and increases again when the water becomes less, as happens for instance during the day when transpiration gets more and more intense. As open stomata are sometimes found even in'wetted plants, the appearance of starch does not so much indicate the closure of the stomata as a diminution of the water content in the guard cells and the leaf as a whole. By employing chloral-hydrate-iodine as a delicate test for starch, I examined the stomata of both kinds of leaves at different times during the day. The corresponding youngest leaves were chosen and the results which were confirmed by repeated observations are as follows, the drawings having been made with the help of the Zeichen Apparate.
The conclusions arrived at are:—
(1) that young leaves with bladders or with a tendency to bladder showed very little starch in the guard cells of the stomata which indicates a high-water content in the leaf.
(2) that leaves without bladders always contained more starch which is doubtless a response to the low-water content of the leaf.
It thus appeared possible that the bladders could be induced to form by making the water aailable to its utmost capacity, and I succeeded in this by growing a plant without bladder in Crone's solution of low concentration, viz., 1 in 1000. Plants were also grown in Sach's solution of normal concentration and in tap-water of the laboratory which is relatively higher in salts. The latter showed no
