450 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Recent researches into the nature of the nucleus carried out 

 by Professor Weissmann and others tend to show that the most 

 important elements in its constitution are certain rod-like fibres, 

 looped threads, or round grains called " chromosomes " (idants of 

 Weissmann), which change their appearance and their position 

 from time to time, but which nevertheless generally remain 

 constant in number in the same species. 



These are present in the nucleus of every cell, but in the 

 germ cells at the time of fertilisation, not only is their position 

 and shape altered, but their number is apparently decreased by 

 one half, and, according to Professor Weissmann's interpretation 

 of the facts in his well-known book, " The Germ-Plasm " (Con- 

 temporary Science Series), the essence of fertilisation consists in 

 the removal of one half of the nuclear elements from the egg cell 

 of the mother and the replacing of them by an equal number 

 from the pollen cell of the father, and in this way Professor 

 Weissmann accounts for the different phenomena of heredity, 

 reversion, and variation, and endeavours to make clear the many 

 mysteries of inheritance which have puzzled philosophers and 

 naturalists from Aristotle to Darwin. 



Later researches seem likely to modify Prof. Weissmann's 

 speculations considerably ; but they are not yet sufficiently 

 advanced to form a definite opinion upon, and we must be 

 content to wait patiently for further facts. 



I am not aware that the number of nuclear fibres in the 

 cells of Orchids has yet been ascertained, but in the closely 

 allied order of Liliacea?, in the plant Lilium Martagon, M. 

 Guignard has recently observed that while the ordinary cell 

 contained twenty-four nuclear fibres the ripe egg cell had but 

 twelve, apparently showing that it was ready for fertilisation. 

 (M. Guignard, Compt. Bend., May 11, 1891, and Nouv. Etudes 

 sur la Fecondation, " Ann. Science Nat. Bot." vol. xiv. 1891, 

 p. 1G3.) So that if we take Cypripedium x Leeanum as our typical 

 hybrid, we find that its nuclear fibres would be made up one 

 half from its parent C. Spicerianum and the other half from its 

 other parent, C. insigne ; both the parents being pure species 

 their own nuclear fibres would of necessity be pure and true 

 (their ancestors for many generations having been the same 

 species as themselves). These nuclear fibres being, as we have 

 een, the bearers of the hereditary characters, and determining 



