Chapter X — 133 — Drosera 



may occur on the under side. Due to the different anatomical struc- 

 ture, the origin is more various, for the epidermis may not in all cases 

 take active part in the earlier cell divisions. These occur usually in 

 the vicinity of stomata or near the bases of trichomes or of sessile 

 glands, but can arise also on the stalk of the inflorescence or even from 

 the latter itself, as axillary buds however (Robinson 1909). Since the 

 flower stalk is radial in structure, the buds arise on all sides, and on 

 account of the closed cylinder of sclerenchyma, they never articulate 

 with the vascular system of the flower stalk. Adventitious buds may 

 arise from roots also, in which case they are, as would be expected, 

 endogenous in origin. 



In the case of D. spathulata Behre found regeneration by bud for- 

 mation to take place indirectly from callus, previously formed on the 

 cut end of a leaf stalk. 



Miss MouLAERT (1937) obtained adventitious buds from leaves, 

 isolated petioles, hypocotyls, stems, scapes, receptacles and sepals. 

 Following the formation of epiphyllous buds, she observed the develop- 

 ment of cushions of tissue ("bourrelets") extending from the base of 

 the plantlet toward the petiole. These are of three kinds, those which 

 remain as mere thickenings in the parenchyma above the veins, and 

 which she called "undifferentiated"; those which act as a liaison be- 

 tween the plantlet and a root which has already differentiated ad- 

 ventitiously nearby and in which a vascular connection between shoot 

 and root becomes established; and third, a kind which is formed near 

 the plantlet which does connect with it, an example of "affolement 

 cellulaire. " 



Another observation made by Moulaert is the occurrence of ab- 

 sorbing hairs, structures quite like root hairs, which arise from the 

 upper surface of the leaf blade or from the basal part of the stem of 

 the plantlet. They are very abundant and their walls are brown as 

 in the case of root hairs. 



Conditions determining the incidence of leaf buds. — It has gen- 

 erally been observed that the production of adventitious buds takes 

 place only under conditions of high humidity, and apparently the 

 higher the better. In order to obtain them the practice is to remove 

 leaves and place them on moist moss, or float them on water, in cov- 

 ered vessels (Graves 1897; Grout 1898; Ames 1899; Robinson 1909; 

 Leavitt 1903; Salisbury 191 5; Vickery 1933, and others). But the 

 matter seems not to be quite so straight-forward as this. Dixon (1901) 

 found that such buds occur on plants in abundance when they have 

 been allowed to dry out gradually on their bed of Sphagnum under a 

 bell-jar, during a period of two months. Confirmatory of this is 

 Behre's observation that leaves which had been removed and sus- 

 pended in a moist chamber, but not so moist as to prevent some wilt- 

 ing, will produce many buds. A too great plenitude of moisture 

 therefore appears to mask a delicate balance of affairs between the 

 leaf and its environment. 



As to temperatures, Ames (1899) thought that low temperatures 

 were favorable. Vickery found a wide favorable range. My own 

 experience favors the idea that D. rotundifolia at any rate is active in 

 this way at prevailing cool temperatures. 



