,8,,. AMBER AND FOSSIL PLANTS. 383 



they fall from the trees after their function has been fulfilled, at 

 a time when resinous exudations would be plentiful, and in a 

 condition suitable for the reception and embedding of foreign bodies. 



The Californian genus Sequoia, the Japanese genera Sciadopitys 

 and Lihocedvus, the Swamp-Cypress (Taxodium distichum) and others 

 afford examples of Conifers lost to Europe since the Tertiary period. 

 In addition to those already alluded to, species occur of Thuja, Abies, 

 Jtmiperites, Picea, Cupvessus and other genera. 



The great majority of the fragments of coniferous wood from the 

 Baltic Amber have been referred to Pinus succinifera, a species whose 

 various tissues have been fully described by Conwentz and previous 

 writers ; in certain anatomical details this species resembles varieties 

 of the recent Conifer Pinus laricio, but in certain points stands alone 

 as a characteristic and extremely common Pine of the Amber Flora. 



From an examination of the forms and structural details of frag- 

 ments or splinters of the wood of Pinus and other trees, it has been 

 shown by Conwentz how it is possible to arrive at conclusions in 

 many cases as to the conditions under which the splinters were 

 formed. For such a work as this a close study of living trees is a 

 necessary preparation. Pieces of wood torn off stems and branches 

 by the impact of falling trees, or broken off by wind, have certain 

 peculiarities in shape and microscopic structure which distinguish 

 them from splinters struck off by lightning : the action of the latter 

 is recognised by the torn membranes of the wood elements, and by 

 the general form of the splinters, the action of wind and falling trees, 

 &c., splits off fragments of wood whose component elements are for the 

 most part whole. 



Occasionally pieces of Amber show distinct signs of burning, 

 suggesting by their charred appearance the burning of forest fires 

 ignited by lightning flashes. In looking through microscopic pre- 

 parations of English Coal-measure plants, one sometimes notices 

 tissues in which the cell-walls are black and apparently charred, 

 strikingly suggestive of the action of fire (9 /3, PI. 33, fig. ig). 



Another phenomenon which is brought out by the microscopical 

 examination of tissues in Amber is named by Conwentz (2) " Ver- 

 grauung." This consists in the loosening or partial separation of 

 tracheids imparting to the surface of the wood a certain woolly or 

 hairy texture. The same phenomenon may be seen on the exposed sur- 

 face of Pine- wood shingles used in the roofs of country houses in the 

 hilly districts of Germany and other countries ; the fresh smooth 

 surfaces after a time lose their freshness and become woolly as the 

 result of this " Vergrauung " process. 



Instances are recorded of double " annual " rings in stems and 

 Amber trees. Among living trees, Kny (5) has described a case of 

 double rings in Tilia pavvifolia, whose leaves were eaten by cater- 

 pillars about the end of June, and this caused a premature develop- 

 ment of the next year's buds. The branches on which these leaves had 



