142 Development of the Natural System under [BOOKI. 



principles of classification in these classes ; he was still more 

 happy in being the first to detect the peculiar structure of the 

 flower of Conifers and Cycads, as compared with that of other 

 flowering plants ; it was he who perceived that what had been 

 hitherto called a female flower in these plants was really a naked 

 ovule, a view which Trew of Nuremberg had, it is true, sug- 

 gested in the year 1767. He also called attention to the 

 agreement in structure of the male and female organs in these 

 families. Thus one of the most remarkable facts in vegetation, 

 the gymnospermy of the Conifers and Cycads, was for the first 

 time established, and this led afterwards through Hofmeister's 

 investigations to the important result, that the Gymnosperms, 

 which had been up to that time classed with Dicotyledons, are 

 to be regarded as co-ordinate with Dicotyledons and Monoco- 

 tyledons, forming a third class through which remarkable 

 homologies were brought to light in the propagation of the 

 higher Cryptogams and the formation of seeds in Phanerogams. 

 No more important discovery was ever made in the domain of 

 comparative morphology and systematic botany. The first steps 

 towards this result, which was clearly brought out by Hof- 

 meister twenty-five years later, were secured by Robert Brown's 

 researches, and he was incidentally led to these researches 

 by some difficulties in the construction of the seed of an 

 Australian genus. He discussed in a similar manner, if not 

 always with such important results, a great variety of questions 

 in morphology and systematic botany ; even purely physiologi- 

 cal problems were raised by him in this peculiar way, and 

 especially the question how the fertilising matter of the pollen- 

 grains is conveyed to the ovule; he had already concluded 

 from the position of the embryo that it is conveyed through 

 the micropyle and not through the raphe and the hilum, as was 

 then supposed, and he was the first also to follow the passage 

 of the pollen-tubes in the ovary of Orchids up to the ovules ; 

 but this is a point which will be more properly considered in 

 the history of the sexual theory. 



