182 The Anatomy of Plants BOOKII 



Our knowledge of the details of the process of karyo- 

 kinesis or mitosis is derived chiefly from the writings 

 of Flemming and Strasburger, who agreed in the main on 

 the course of events occurring, though certain points of 

 difference were observed. They were, however, compara- 

 tively unimportant. 



The longitudinal fission of the chromosomes was dis- 

 covered by Flemming in 1880. He also first described the 

 heterotype division in 1887. 



The reduction division associated more or less directly 

 with the sexual nuclei, was first observed by Van Beneden 

 in 1883, and again in 1887, occurring in the germ cells of 

 Ascaris. It was discovered in plants by Overton in 1893 

 when studying the endosperm of Ceratozamia, and in the 

 same year by Dixon, who observed the reduced number in 

 the endosperm of Pinus. The great generalization that the 

 nuclei of the gametophyte give rise to only half the number 

 of chromosomes that characterizes those of the sporophyte 

 was made by Strasburger in 1894. He was confirmed by 

 Farmer's researches on the liverworts made later in the 

 same year. 



The years 1858-63 were noteworthy for the elaborate 

 researches of Naegeli on the constitution of cell walls, 

 starch grains, and other organized bodies, on which he based 

 his views of their structure and of their growth by intussus- 

 ception. These views were stated very fully by Sachs in 

 his History of Botany (English ed., p. 350), so that a summary 

 of them is all that is needed here. They met with his 

 strong approval and support, and indeed led him almost 

 to the view that they represented finality on the subject. 

 They were accepted almost without challenge for more 

 than twenty years. 



On Naegeli's hypothesis the cell wall, like the starch 

 grain, consists of crystalline particles between which water 

 penetrates ; they are solid and relatively unchangeable, 



