INTRODUCTION '^-CJ!^ 



From the days of Nehemiah Grew and Robert Hooke to the time of 

 Matthias Schleiden and Herman Schacht, histological technique was 

 in a very primitive condition, each investigator making his own micro- 

 scope and other apparatus. Stems and similar objects were held in 

 the hand and cut with sharp knives, while things which did not lend 

 themselves to such technique were dissected with needles, even such 

 difficult objects as embryo sacs and embryos being teased out so that 

 fairly accurate views were obtained. Schleiden's cell theory (1838), 

 the "theory" that a plant consists entirely of cells, was developed 

 from such preparations. 



Carl Zeiss, one of Schleiden's students, dissatisfied with his micro- 

 scope, quit the study of botany and proceeded to improve microscopes. 

 His success gave the scientific world immensely better microscopes, 

 and the better microscopes brought improvements in histological tech- 

 nique. By 1850, stains were being used, and improvements came so 

 fast that a history of technique, rather than the practice of it, would be 

 needed if one were to trace the whole subject. Before the end of the 

 century, there were numerous fixing agents, paraffin baths, and micro- 

 tomes, and staining had reached a high degree of efficiency. 



Unfortunately, some of the skill of the older botanists in teasing 

 material and studying it in the living condition had been lost; but this 

 valuable phase of technique is being revived and, with the micro- 

 manipulator, results are being obtained which surpass the wildest 

 dreams of Schleiden and Strasburger. 



In the fourth edition we stated that the pollen grain of a hly, placed 

 on a dark background, is barely visible to the naked eye; but with 

 modern technique, such a pollen grain can be cut into fifty sections, 

 the sections can be mounted and stained without getting them out of 

 order, a photomicrograph can be made from the preparation and a 

 lantern slide from the photomicrograph, and finally there appears on 

 the screen a pollen grain 10 feet long, with nuclei a foot in diameter, 

 nucleoli as large as baseballs, and starch grains as large as walnuts. 



While this is a striking illustration, modern technique shows its 

 efficiency better in demonstrating the structure of chromatin and the 



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