254 SUMMARY OF CURRENT RESEARCHES RELATING TO 



heterophylly, when it depends on something inherent in the organization, 

 or of aniaophylly, when it is the result of a difference of position, as in the 

 case of aquatic plants where tbe floating and the submerged leaves differ 

 in form. In tbe former case the cause is unknown, and the two kinds 

 of leaves may pass into one another by insensiblo gradations, as in 

 Broussonetia and Morns. Both may be the result either of progression 

 or of retrogression. 



Colours of Leaves and Fruits.* — Tlerr A. Wigand has investigated 

 tbe nature and the cause of the red and blue colours of a large number 

 of leaves and fruits. Ho classifies the very numerous examples men- 

 tioned under a number of heads. In many plants the stem and leaves 

 exbibit normally and constantly a red or blue colour in the form of 

 streaks or spots. In others, especially woody plants, it appears only as 

 the branches and leaves unfold ; in the " copper " varieties of trees, such 

 as tbe ash, beech, hazel, or elm, it increases in intensity as the leaves 

 dcvclopo ; while in others it appears only in the autumn, and either in 

 connection with the dying of the leaves or not. Many plants exhibit 

 these colours only locally as the result of injury, especially puncture by 

 insects. In many fruits, especially such as are fleshy, the red or blue 

 colour appears only during ripening, and then obviously depends on tbe 

 influence of light. Many rhizomes also exhibit a red colour. 



Tbe colour generally preponderates on the upper side of the leaf, or is 

 limited to that side ; usually it is contained only in the cell-sap ; less 

 often it colours also tbe cell-walls. Tbe seat of tbe red colour may be 

 either the epidermis, the parenchyma, or the vascular bundles ; the order 

 in which it makes its appearance is always : — (1) the veins, (2) tbe 

 epidermis, (3) tbe parenchyma. 



The colour of most ripe berry-like fruits is due either to insoluble 

 pigment-particles, or to a homogeneous colouring of the cell-sap. It is 

 not in any way due, as some have maintained, to a modification of 

 chlorophyll. Some plants with coloured stems, e. g. Cuscuta, contain 

 erythropbyll, but never chlorophyll. The colouring matter may be 

 contained in different cells from tbe chlorophyll, or in the same. The 

 chromogen or colouring constituent of tbe pigment the author believes 

 to be a form of tannin. 



Alpine vegetation is especially characterized by the tendency to a 

 red colouring. The author considers that the conditions specially 

 favourable to the production of either red or blue colour are a feeble or 

 completely suppressed assimilation and a strong light. 



Anatomy of the Floral Axis.f — Herr K. Eeiche gives details of 

 several points of structure in the axis of flowers, and of inflorescences, 

 especially in connection with the contrast between tbose of male and of 

 female flowers. In Cueurbita Pepo the female flower-stalk is distinguished 

 from the male by its greater thickness, and by its strong bicollateral 

 vascular bundles containing cambium, while the much smaller bundles of 

 the male flower-stalks have no cambium ; both kinds have a hypodermal 

 ring of collenchyma. In other cases the chief characteristic of tbe female 

 as contrasted with that of tbe male axis, is the larger quantity of starch- 

 containing tissue. This is strikingly the case in Mercurialis perennis, 



* Wigand's Bot., Hefte ii. (1887) pp. 218-43. 



t Ber. Deutsch. Bot. Gesell., v. (1887) pp. 310-8 (1 pi.). Cf. this Journal, ante, 

 p. 79. 



