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Periods. The specimens in this case complete the sequence 

 of plant life on the earth and bring it up to modern times. 

 A number of specimens at one end of the case show the 

 methods of preservation by petrifaction, incrustation and 

 carbonization and on the upper shelf is a series of speci- 

 mens from Quaternary and more recent swamp deposits which 

 show how the conversion of living plants into fossils, a 

 process now going on, has its beginning. 



The specimens in the adjoining wall-case further illustrate 

 the characteristics of the plants of the late geological periods 

 and the methods by which the various plant structures have 

 been preserved. 



A number of specimens of silicified woods show the method 

 of preservation by what is known as petrifaction, or conversion 

 into stone, in which the woody structure is replaced by mineral 

 matter. Other specimens show preservation by incrustation, 

 in which mosses and the stems of reeds are coated or incrusted 

 by mineral matter deposited from springs ; while on the upper 

 shelf and on the top of the case are logs and stumps from old 

 swamps and interglacial deposits, in which the wood has been 

 partially carbonized, or converted into lignite, by the slow 

 process of natural distillation. This process represents the 

 beginning of the conversion of vegetable tissue into coal. 



LECTURES 



Other features of the museum building include the large 

 public lecture hall, with a seating capacity of over seven 

 hundred, which occupies the western end of the basement. It 

 is equipped with an electric projection-lantern, and public 

 popular lectures covering a wide field of botanical and horti- 

 cultural subjects are delivered here on Saturday afternoons 

 in autumn and spring ; these are fully illustrated by means of 

 a very extensive collection of lantern slides owned by the 

 Garden which is constantly being increased ; a noteworthy 

 part of this collection is the series of delicately and accurately 

 colored slides of flowers, fruits, trees and shrubs, by Mrs. 



