PREFACE 



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During and since the great world war there has been a growing demand 

 for information on the injurious and useful plants of America. The in- 

 jurious plants are represented by those belonging to the lower phyla, the 

 thallophytes, which include the fungi, destructive to farm crops, and the 

 higher flowering plants, which are some of them also injurious. In 

 the following pages, particular attention will be given to the flowering 

 plants with casual mention of the flowerless forms, which come within the 

 i purview of this book. The contents of the pages, which follow, epitomize 

 ^ the laboratory and research work of the writer connected with a course in 

 J botany given to the veterinary students of the University of Pennsyl- 

 \ vania for the past twenty-five years. The course has been given during 

 the college year for two hours per week, one lecture and one laboratory 

 hour. The first term (October to February) is devoted to a study of the 

 general morphology and physiology of plants, and the second term (Febru- 

 ary to June) to the consideration of the plants (injurious and useful) of 

 economic importance. The laboratory exercises supplement the lectures. 

 The injurious plants are considered first, because they lend themselves 

 culiarly to indoor laboratory work of a technical kind, which can be 

 M pursued in the northern states, while wintry conditions prevail out of doors. 

 S Then too, professional students are anxious after the preliminary work 

 has been given, such as the morphology and physiology of plants, to start 

 ^ at once upon the part of botany which applies directly to the scientific 

 V\ preparation for their life's work. The study of the stock-killing and 

 ^poisonous plants with the medical applications does this in a peculiar way. 

 v\\ These two reasons are the ones which determined the placing of the tech- 

 ^Vsnical laboratory methods first in the arrangement of the subject matter 

 ^ of this text-book. The study of the forage plants (grasses and legumes), 

 of the weeds and of seed testing, which are presented in the final chapters of 

 the book, is pursued naturally most satisfactorily, when the weather 

 conditions permit the gathering of fresh material for lecture and labora- 

 tory 'purposes, and when to some extent outdoor work is made possible 

 and pleasant. The teacher in the southern states, or on the Pacific slope, 



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