Examination of Cell-membrane in Plants. 257 



that the examination of the internal structure of plants, as well 

 as the describing them according to Linnaean patterns, was a 

 part of botanical enquiry ; it is at the same time true that the 

 botanical knowledge of these observers was often of service to 

 them in their phytotomical investigations, and directed their 

 work decidedly and from the first towards that which was 

 worth knowing, and towards the objects which claimed the first 

 attention. This remark applies to the younger Moldenhawer 

 even more than to the botanists above-named ; his ' Beitrage,' 

 published in 181 2, may be taken as closing the first section of 

 this century, during which time he improved the methods of 

 observation, compared his own observations and those of 

 others with great acuteness of judgment, and did all that could 

 be expected with the microscopes of the time. 



The period of sixteen years after Moldenhawer, from 181 2 

 to 1828, has nothing of material importance to show in 

 phytotomy. On the other hand, it produced a series of the 

 most important improvements that the compound microscope 

 has undergone since its invention. 



As early as 1784 Aepinus had produced objectives of flint 

 and crown glass, and in 1807 Van Deyl 1 made similar ones 

 with two achromatic lenses, and still the phytotomists com- 

 plained of the condition of their instruments. Their figures show 

 that they could not see clearly with them, though the magnify- 

 ing powers were not high ; Link says expressly in the preface 

 to his prize-essay of 1807, that he usually observed with a lens 

 that magnified a hundred and eighty times. Moldenhawer 

 in 1 81 2 gives the preference over all the microscopes he had 

 used to one by Wright, which was serviceable with a magnify- 

 ing power of four hundred times, while the German instruments, 

 especially those by Weickert, could not be used with higher 

 powers than from one hundred and seventy to three hundred. 



A certain interval elapsed each time between an improvement 



See P. Ilarting, ' Das Mikroskop/ § § 433 and 434. 



S 



