INTRODUCTION AND HISTORICAL BACKGROUND 3 



activity if only we can read them aright. Further, and of more im- 

 mediate importance, forming as they do an outer envelope surrounding 

 each little unit of protoplasm in the plant body and remaining so from 

 the beginning during the whole of its life, they can hardly fail to be 

 vitally concerned in the increase in bulk of cells and tissues and to carry 

 with them a record of cellular activity. It is from these points of view, 

 and these alone, that this book has been written. 



The astounding progress during recent years in the whole field of 

 structure in biological materials, using the methods which modern 

 physics has placed in our hands, is perhaps sometimes apt to blind us 

 to the very solid foundation which our distinguished predecessors have 

 laid with their completely inadequate tools, and upon whose firmness of 

 construction our ivory towers depend. It is therefore a salutary lesson 

 to go down and consider, even if very briefly, the stones — and the 

 rubbish — which lie in the basement. The historical period concerned 

 can be divided roughly into four sub-periods — the period before the 

 discovery of the microscope, of which we shall have nothing to say, the 

 period from the first use of the microscope in about 1666, to the 

 application of the polarizing microscope in about 1830, the period from 

 this time until the year when the method of X-ray analysis began to 

 develop, and the modern period since that time. 



The beginnings of cell wall studies 



It was naturally only after the improvement by Robert Hooke of the 

 microscope recently devised by the Janssen brothers, to give reasonable 

 magnification with tolerable definition, that anything useful could be 

 written about our subject. Although Henshaw is said to have discovered 

 the vessels in the wood of walnut trees as early as 1661, the study 

 properly begins with the publication by Hooke of his Micrographia 

 (1667) and the drawing which he there published, and as so often 

 figured in later treatises of elementary botany, of cell structure in cork, 

 Hooke, however, was not in any sense a botanist and contented himself 

 with the description of the honeycomb structure he perceived and with 

 fanciful comparisons with bone-lace. The few years which followed, 

 however, saw rapid advances though almost solely at the hands of 

 two investigators, Malpighi in Italy and Grew in England. These two 

 together laid the foundation of all that was known concerning cellular 

 structure for the next hundred years. Grew in particular, though his 

 presentation lacked the tasteful elegance of Malpighi, produced a mass 

 of minute detail on the anatomical features of plants, and we shall 

 confine our attention to him for that reason. Among the many cell 



