432 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Mechanism of Fruits for the Purpose of Dispersion.* — Herr G. Eichholz 

 describes the arrangement in a number of fruits by means of which the 

 bursting or twisting is brought about which promotes the dispersion of 

 the seeds. This is generally effected by the adaptation of certain cells, 

 either from their first formation or shortly before they become ripe. These 

 special cells may be arranged in two groups, according as they contract 

 most strongly, on desiccation, in the longitudinal or in the transverse 

 direction. The curve in the tissue resulting from unequal contraction of 

 these elements may be either double or single ; and in the latter case may 

 result from contraction of the concave or from elongation of the convex side. 



As regards the details of the structure in special cases : — In Impatiens 

 the layer of pericari) which swells is a mechanism resembling a bladder 

 which is drawn out by hydrostatic pressure. The change of form of the 

 cells determines the direction, the great extensibility of the membranes 

 the extent of the expansion. The fibrous or resisting layer has very little 

 flexibility, but gi-eat traction. In Eutaceae the eudocarp has a hinge- 

 structure. In Dictamnus, but not in Buta, the endocarp is thrown out 

 together with the seeds. In the Eutaceas, Liliacefe, and Ehodoreae the 

 curvature is brought about by the dynamo-static elements being placed trans- 

 versely on the concave, vertically on the convex side. In Fagus, Ejjilohium, 

 and Datura, the thin- walled parenchyma is the contracting tissue. In 

 Epiluhhnn the median vascular bundle takes no part in the contraction. 

 In Pinus, Eschscholtzia, Acacia, Acanthus, and Scandix, the curvature is the 

 result of a constant difference in the direction of the pores in the fibrous 

 elements. The isodiametrical thick- walled cells of }Vei'jela, Azalea, and 

 Ehododendron have two functions ; they contribute to the curvature in a 

 vertical plane ; and they cause also the curvature in a horizontal plane, 

 which is essential for the jierfect release of the seeds. The isodiametrical 

 cells of Primula exercise a traction in the vertical direction only. 



/3. Physiology. t 

 (1) Reproduction aud Germination. 



Fertilization of Orchidese.:!: — M. L. Guignard confirms the statement 

 of previous observers that the formation of the ovules in Orchideaj is the 

 result of the activity of the pollen-tubes. 



In Vanilla aromafica the pollen-grains germinate a few hours after 

 being placed on the stigma, which is covered by a gelatinous secretion. 

 The ovary, which, at the period of pollination, is about 4 cm. long, 

 immediately begins to lengthen, until it attains a length of about 20 cm. 

 At the same period the oviiles have merely attained the state of small 

 papillae on the placenta. On the fifth or sixth day after pollination the 

 nucellus is visible at the summit of the papilla, which then begins to curve 

 on the funicle. On the eighth day the inner integument begins to be formed 

 by division of the epidermal cells ; the formation of the outer integument 

 follows, and the mother-cell of the embryo-sac increases in size at the 

 summit of the nucellus beneath the epidermis. On the twelfth day the ovule 

 has become anatropous ; the internal coat reaches almost to the summit 

 of the nucellus ; the outer coat is still very short, but passes the internal coat 

 about the twentieth day. During this time the mother-cell of the embryo- 



» Pringiheim's Jahrb. f. Wise. Bot., xvii. (1886) pp. 543-90 (4 pis.). 



t This subdivision contains (1) Reproduction and Germination; (2) Nutrition and 

 Growtli; (3) Movement; and (4) Chemical Ciianges (including Respiration aud 

 Fermentation). 



X Aun. Sci. Nat. (Bot.), iv. (188G) pp. 202 40 (2 pis.). Cf. this Journal, 1883, p. 84. 



