PREFACE 13 



with a razor is of no further use to anyone unless 

 he becomes a professional botanist (of no very great 

 use indeed to many professional botanists), and to 

 acquire any useful proficiency occupies far more time 

 than it is worth, when the student's hours are strictly 

 limited. 



With a small class and ample time the case is quite 

 otherwise, and not only should students cut many 

 of their own sections under these conditions, but 

 they may be taught to prepare material and experi- 

 ments with great advantage to themselves and to their 

 ultimate grip of the subject. Such conditions, however, 

 simply do not exist in big university classes with 

 every hour of the student's working day filled up. 



In the earlier schedules, especially, fairly precise 

 instructions are given to the student, and some general 

 hints are prefixed to the book (p. 17), suggested by 

 experience of the mistakes students most frequently 

 make in doing their practical work. They are of 

 course intended only for those who have no previous 

 experience of microscopic work in the laboratory. 



It is believed that the actual measurement of 

 microscopic objects, though not usual in elementary 

 classes, is a valuable help to the student in relating 

 the structures he sees under the microscope to the 

 objects he sees with the naked eye, giving the former 

 a greater objective reality in his mind. It is therefore 

 suggested that the student should learn early in 

 the course to calibrate a micrometer eyepiece with a 

 micrometer slide, and that he should frequently 

 measure the diameters of microscopic objects. 



I am greatly indebted to my daughter Margaret, 

 who has drawn the whole of the illustrations. The 



