158 THE PATH OF SCIENCE 



It was not until the seventies that the Swiss scientist Hermann 

 Fol actually saw the spermatozoon of the starfish enter the 

 egg and thus showed for animals, as Pringsheim had shown 

 for plants, that fertilization consists of the fusion of two cells. 



Meanwhile, the fundamental principles of the reproduc- 

 tion of plants were at last being discovered. A considerable 

 obstacle had to be overcome before progress could be made 

 in this subject. It had been supposed, quite naturally, that 

 the ovule was to a plant what the egg is to an animal. It was 

 an amateur botanist ^vho made all the fundamental discov- 

 eries that exposed the falsity of this view. Early in the fifties 

 Wilhelm Hofmeister, a music-seller, showed that mosses and 

 ferns exhibit an alternation of generations: that the spore of 

 a fern plant does not grow into another fern but into a com- 

 pletely different kind of plant, which itself reproduces sex- 

 ually to produce the fern plant once more. That was remark- 

 able enough, but Hofmeister went straight on to show that 

 there is an exactly comparable alternation of generations in 

 the flowering plants: part of the ovule is actually another 

 generation living parasitically on the parent that produced 

 it. This was one of the most important botanical discoveries 

 ever made, and it was all the more noteworthy because Hof- 

 meister did his work at a time when the actual process of 

 fertilization was not understood in either plants or animals. 

 Hofmeister, who was self-taught and had had no academic 

 training, now became a professor of botany at a great Ger- 

 man university. 



Attention now began to be focused on nuclei. When 

 nuclear division occurs, chromosomes become apparent. 

 Chromosomes are colorless and transparent, but they have 

 an intense affinity for many ordinary dyes. Indeed, it is for 

 that reason that they are called by a name that means color 

 bodies. They had been glimpsed by Karl Nageli early in the 

 forties; now, owing to the rediscovery of staining, they had 

 become one of the easiest things in the cell to study. In the 

 seventies the German botanist Eduard Strasburger made out 

 the principal features of nuclear division in plants, and shortly 



