SCIENCE-GOSSIP. 



107 



broken, and huge rock masses hang from them in 

 positions of the most precarious stability. At the 

 cave's mouth the waters of the Mediterranean 

 seethe and hiss around the sunken boulders, and 

 even on the calmest day as these sounds rever- 

 berate through the darkest passages they never 

 fail to excite in one's mind feelings of the most 

 awesome insecurity. 



Within the cavern's depths a very representative 

 collection of Tortonian fossils may be obtained 

 from the water-sodden limestones with the aid of 

 a stout pocket-knife. The differential erosion to 

 which the various strata have been subjected has 

 caused the entombed sea-urchins, corals, shells 

 and other fossil organisms to stand out in bold 



relief from their comparatively soft limestone 

 matrices. Between L'Ahmar and the northern 

 shore line the country has a very rugged and 

 barren aspect. Neither tree nor shrub is to be 

 seen anywhere. The greater portion of this part 

 of Malta is a barren, sandy, rocky waste, with an 

 integument of soil so thin and arid that little save 

 the Mediterranean heath, Erica peduncularis, and 

 the marine plant, Crucianella maritima, have been 

 able to establish a footing in it. 



It is a dreary, desolate region, that is seldom 



visited by anyone, except in the sporting season, 



when the wild duck, snipe, plover and quail frequent 



the islands en route for the neighbouring continents. 



{To be continued.) 



TREES OF DAMP AND DRY PLACES. 

 By Dr. P. Q. Keegan. 



T T seems to be even more firmly established and 

 generally admitted with respect to plants than 

 animals, that the existing form of a species is 

 determined by two factors, viz., the inheritance of 

 the properties of its ancestors, and the changes 

 which these properties undergo through the 

 influence of the environment. The existing form 

 of a forest tree, for example, is the result of the 

 conjoint operation of these two causes ; but it is 

 here contended that, while the external influences 

 can modify the form or the dimensions of the 

 structural elements (vessels, fibres, parenchyma) 

 of its wood, on the other hand the relative arrange- 

 ment of the various elements and the fundamental 

 economy of the woody plan are strictly and solely 

 the more or less immutable property of the species 

 as inherited from its ancestors. For instance, the 

 majority of our forest trees possess in their wood 

 only a single kind of medullary rays, but the oak 

 has two different kinds of these. The beech, 

 again, possesses more than three thicknesses of 

 cells in many of its medullary rays, while most of 

 our other trees produce only from one to three 

 thicknesses of cells in these organs. So also with 

 respect to the vessels : those of the alder and birch 

 are numerous and ample ; while, on the contrary, 

 these elements are rare and isolated in the Spanish 

 chestnut. All these distinct and decided differences 

 in respect to the greater or less development of the 

 parenchyma of the wood (the medullary rays) 

 called, very significantly, the " fundamental tissue," 

 and in respect to the general number and distribution 

 of the vessels called, very truly, the "essential 

 elements " of the woody bundles, must be regarded 

 as indissolubly bound up, as it were, with the inner 

 life of each particular species of tree. They remain 

 fixed and unalterable wherever it may happen to 

 grow : whether the soil be dry and sandy or moist 



and clayey, whether by the river side or in the cleft 

 of a hard rock, or whether the predominant state 

 of the air be moist, dry, chilly or sunny — it is all 

 the same. The physical forces of nature which 

 encompass the plastic arboreal organism replete 

 with life and energy cannot mould it beyond a 

 certain point, cannot interfere with or prevail over 

 the fixed immutable rules which guide its growth 

 and inevitably ordain the direction thereof. The 

 hereditary characters which its parents have 

 handed down to it in the sequence of existence 

 are strictly conservative. Heredity is preservative, 

 accumulative, and not destructive in any sense. 



Yet, while all this is so, another most potent 

 influence is actively at work within the veil of 

 mystery that hangs over the inner life of the 

 woodlands. This is the struggle of the organism 

 to adapt itself to its environment. To see any 

 particular species of tree, such as an elm or hazel, 

 growing sometimes in a damp swamp, or sometimes 

 in a high and dry locality, is a common experience. 

 Then again, it is well known that certain trees 

 thrive best, seem to do well indeed, only in humid 

 places where both air and soil are moist : as, for 

 instance, alder, willow, ash, maple, sycamore — and 

 this on account of the great transpiration from 

 their leaves. The structure of their wood, how- 

 ever, in so far as regards the forms and dimensions 

 of its elements, is adapted to the circumstances. 

 Where moisture of the soil stands in greatest 

 need, there the wood is poor in the number of its 

 fibres, the vessels are very numerous, the medullary 

 rays are small and narrow, while there is no 

 sensible difference in density between the wood 

 formed in autumn and that formed in spring-time. 

 On the other hand, the wood of elms, hazels, etc., 

 which affect a dry station, is characterised by an 

 increase in the number of its fibres, whose walls, 



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