(124) 
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 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 free 
public popular lectures covering a wide field of botanical 
and horticultural subjects are delivered here on Saturday 
afternoons from spring to autumn; 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. Adelaide S. Van Brunt, from photographs 
made during many years by her late husband, Cornelius 
Van Brunt. 
The Horticultural Society of New York holds several of 
its monthly meetings at the Garden, using the large lecture 
hall, and also uses the basement museum hall adjacent for 
the purpose of exhibitions. 
The Torrey Botanical Club holds monthly meetings from 
October to May, on the afternoon of the last Wednesday of 
each month, in the museum building, and several of its field 
