Chap, in.] the Dogma of Constancy of Species. 141 



His most valuable work in this direction is a paper on a genus 

 Kingia, discovered in New Holland in 1825 ; the structure of 

 the seeds in this genus led him to seek more accurate knowledge 

 of the unfertilised ovule in the Phanerogams generally, and 

 especially in the Cycads and Conifers. In spite of the labours 

 of Gartner and the later researches of Treviranus, there was still 

 considerable obscurity attaching to the theory of the seed, for 

 no one had yet succeeded in referring the position of the embryo 

 in the ripe seed to a general law. For this it was necessary to 

 submit the ovule before fertilisation to careful examination, and 

 Robert Brown carried out this first step to a history of develop- 

 ment with great success ; he was the first to distinguish the 

 integuments and the nucleus in the ovule, and the embryo-sac 

 in the nucleus, parts which Malpighi and Grew had indeed 

 observed but had not brought out with perfect clearness. The 

 micropyle and the hilum of the seed had not yet been properly 

 distinguished, but had been to some extent even confounded 

 with one another. Robert Brown showed that the hilum 

 answers to the point of attachment of the ovule, while the 

 micropyle is a canal formed by the integuments of the ovule 

 and leading to the summit of the nucleus ; that in anatropous 

 ovules the micropyle lies beside the hilum, in orthotropous 

 ovules opposite to it ; that the embryo in the embryo-sac 

 (amnion) is always formed at the spot which lies nearest the 

 micropyle, and that the radicle of the embryo is always turned 

 towards the micropyle, — facts which at once established the 

 general rule by which to determine the position of the embryo 

 in the seed and in the fruit. He also gave the first correct 

 explanation of the endosperm as a nourishing substance formed 

 inside the embryo-sac after fertilisation, and more than this, he 

 was the first to distinguish the perisperm as a substance formed 

 outside the embryo-sac in the tissue of the nucleus. 



In this way Robert Brown established morphological rela- 

 tions in the organisation of the seed of the Monocotyledons 

 and Dicotyledons, which count among the most important 



