179 



THE PLANT CELL: A HISTORICAL 

 SKETCH. 



AGNES ROBERTSON, D.Sc. 



Cytology, the stud}^ of the cells, or elementary units of which 

 all living- things are built up, is a comparativel}' young- science, 

 dating back less than three centuries. Some branches of botany 

 are comparatively independent of special methods of observa- 

 tion. For instance, the systematic botany of flowering plants 

 may well be studied with no external aids at all ; with 

 Cytology on the other hand the case is quite different. We 

 can have no knowledge whatever of cell structure without 

 the aid of lenses, and each fresh development of the subject 

 has had the way paved for it by some fresh development 

 in optics. Some of the first observations with magnifying 

 glasses of which we have a record are those of the Dutch- 

 man Leeuwenhoek (1632- 1723) who examined an infusion of 

 pepper with the aid of lenses, and saw minute living creatures 

 swimming in it. Many people were sceptical about Leeuwen- 

 hoek's results, to his great indignation. ' I have often heard,' 

 he says, ' that many persons dispute the truth of what I advance 

 in my writings, saying that my narratives concerning animal- 

 cules, or minute living creatures, are merely my own invention. 

 .... For my own part, I will not scruple to assert that I can 

 clearly place before my eye the smallest species of these 

 animalcules concerning which I now write, and can as plainly 

 see them endued with life, as with the naked eye we behold 

 small flies, or gnats sporting in the open air, though these 

 animalcules are more than a million degrees less than a large 

 grain of sand. For I not only behold their motions in all 

 directions, but I also see them turn about, remain still, and 

 sometimes expire ; and the larger kinds of them I as plainly 

 perceive running along as we do mice with the naked eye. 

 Nay, I see some of them open their mouths, and move the 

 organs and parts within them ; and I have discovered hairs at 

 the mouths of some of these species, though they were some 

 thousand degrees less than a grain of sand.' In justice to 

 Leeuwenhoek, I ought to explain that when he uses the size of 

 a ' grain of sand ' as a term of comparison, it is by no means as 

 vague as the size of a ' lump of chalk ! ' In the days when 

 hour-glasses were universal, the different qualities of sand 

 were most carefully sifted, and our author explains somewhere 



1906 June I. 



