A LABORATORY MANUAL IN PRAC- 

 TICAL BOTANY. 



INTRODUCTION. 



GOOD authorities estimate that there are more than one 

 hundred and fifty thousand species of plants. In the 

 study of this vast number of different forms we need a 

 framework to build on that will give form and substance 

 to our ideas, placing the facts acquired in positions where 

 we shall be able to find and use them. In the following 

 pages the practical studies have been made to take their 

 appropriate places in a brief outline of classification, to the 

 end that the student's knowledge may assume definiteness 

 of form. 



Many and various schemes of classification have been 

 employed, which differ more or less in accordance with 

 the varying ideas of different investigators, and because 

 of the impossibility of agreement as to the position of 

 certain forms. In the case of the Flowerless Plants, the 

 difficulties of classification are especially great. New 

 plants are frequently discovered. New facts come to 

 light about known organisms which sometimes show that 

 forms which have been considered as separate plants are 

 really only different stages in the development of a single 

 plant ; and points that have been considered as fixed in 

 the classification become unsettled. Any classification, 

 especially in the case of the lower groups, must, there- 

 fore, be looked upon as merely provisional, and subject to 



7 



