138 PLANTS WITH TRAPS AND PITFALLS TO ENSNARE ANIMALS. 



is unable to do this, as the air in the chinks and crannies of its matrix of soil is 

 generally saturated. The water is therefore excreted in liquid form by a special 

 mechanism. 



This view of the function of the scales is confirmed by reference to other allied 

 types with subterranean scales. An instance in point is afforded by Bartsia alpina. 

 This remarkable plant is distributed in the Arctic region and amongst the high 

 mountain flora throughout almost the whole of Europe, and is very striking owing 

 to the colour of its foliage being a mixture of black, violet, and green. The flower, 

 too, is of a sombre dark- violet hue, and the entire plant, by reason of this peculiar 

 colouring, gives a truly funereal impression. We may remark incidentally that 

 the name Bartsia was chosen by Linnaeus for this sad-hued plant as an expression 

 of his own grief at the death of the zealous naturalist and physician, Bartsch, who 

 was his intimate friend, and who succumbed at a comparatively early age to the 

 climate of Guiana. Damp black earth in the neighbourhood of springs constitutes 

 the favourite habitat of these plants. Upon digging in summer time down to their 

 roots, one sees that a few suckers proceed from them, and fasten upon the sedges 

 and other plants growing in the vicinity; but one also discovers subterranean shoots 

 having "root-hairs" developed near the nodes, at which are inserted the paired 

 white scales; and these "root-hairs" have the function of absorption-cells. To- 

 wards the autumn, oval buds, likewise subterranean, are matured, in form not 

 unlike horse-chestnut buds (see fig. 25 5 ), and composed of etiolated scales arranged 

 in four rows and overlapping one another like tiles, so that only the back of the 

 upper part of each scale is visible, the lower part being covered by the scale next 

 beneath it. 



On the visible part of each scale's convex under surface three sharply projecting 

 ribs are noticeable near the middle, whilst the two margins are rolled back so as 

 to form a recess in each case. But, as may be seen in the cross-section of a Bartsia 

 bud (see fig. 25 6 ), one pair of scales lies over the next higher pair in such a way as 

 to convert the recesses into ducts. Owing to this construction the interior of the 

 bud is perforated by twice as many ducts as there are covered leaf-scales, and the 

 orifices of each pair of ducts occur at the spots where the evolute margins of one 

 scale begin to be covered by the middle of the next lower scale. On one wall of 

 the ducts, i.e. in the recesses, structures like those which occur in the cavities of 

 Lathrcea are developed, i.e. stalked glands, each composed of two cells borne upon 

 a basal cell; secondly, pairs of hemispherical domed cells; and, lastly, ordinary flat 

 epidermal cells (see fig. 25 7 ). There can be little doubt that the whole apparatus 

 acts in the same way as in Lathrcea, and is adapted to the excretion of water. The 

 cavities and spaces between the scales of the buds serve the same purpose as the 

 chambers in the leaves of Lathrcea, viz., that of affording cover to the delicate 

 excretory glands and of protecting them from immediate contact with the soil. 



Mechanisms of this sort are not restricted to subterranean organs, but are found 

 likewise on the aerial leaves of many plants. Indeed such arrangements, supple- 

 menting ordinary transpiration, are common, especially amongst tropical plants. 



