3;o Introduction. [Book in. 



logic, and the sexuality of plants was once more openly im- 

 pugned in the face of Koelreuter's investigations. This state of 

 things continued till some time after 1820, but then it began 

 to improve once more. L. C. Treviranus examined and 

 refuted the errors of Schelwer and Henschel in 1822 ; in Eng- 

 land Herbert conducted new and very valuable investigations 

 into the question of hybridisation ; and it was in this period 

 that Carl Friedrich Gartner studied and experimented on 

 normal fertilisation and the production of hybrids during more 

 than twenty years ; his conclusions, published in exhaustive 

 works in 1844 and in 1849, finally settled the more important 

 questions connected with the sexual theory about the same 

 time that Hofmeister established the microscopic embryology 

 of Phanerogams on a firm foundation. 



Other parts also of vegetable physiology had been consider- 

 ably advanced before 1840 ; Theodore de Saussure observed 

 in 1822 the production of heat in flowers and its dependence 

 on respiration ; ten years later Goeppert proved the rise of tem- 

 perature in germinating and vegetating organs. Dutrochet 

 stimulated enquiry by his researches in various branches of the 

 science between 1820 and 1840; he was the first to apply the 

 phenomena of diosmosis to the explanation of the movement of 

 sap in plants with a lasting influence on the further progress of 

 physiology. Chemical investigations were less fruitful in 

 results, though they served to collect a considerable material of 

 single facts, which could afterwards be turned to theoretical 

 account. 



The close of this period, which began with unprofitable 

 doubts, but in which much was set in a train for further 

 development after 1840, is marked by the publication of 

 some important compilations, in which all that had as yet 

 been done in vegetable physiology was presented in a con- 

 nected form. In addition to Dutrochet's collected works (1837) 

 three comprehensive compendia of vegetable physiology made 

 their appearance, one by De Candolle, which was translated 



