10 INTROBUCTION. 



largely on many of the species in this, as well as in 

 the next or dioecious class, being fertilised by the 

 aid of the wind; * for the male flowers have in this 

 case to produce a surprising amount of incoherent 

 pollen. Some few monoecious plants consist of two 

 bodies of individuals, with their flowers differing in 

 function, though not in structure; for certain indivi- 

 duals mature their pollen before the female flowers on 

 the same plant are ready for fertilisation, and are called 

 proterandrous ; whilst conversely other individuals, 

 called proterogynous, have their stigmas mature before 

 their pollen is ready. The purpose of this curious func- 

 tional difference obviously is to favour the cross-fertili- 

 sation of distinct plants. A case of this kind was first 

 observed by Delpino in the Walnut {Juglans regia), and 

 has since been observed with the common Nut (Corylus 

 avellana) . According to H. Miiller, the individual 

 plants of a few hermaphrodite species differ in a like 

 manner; some being proterandrous and others pro- 

 terogynous. f On cultivated trees of the Walnut and 

 Mulberry, the male flowers have been observed to abort 

 on certain individuals,! which have thus been converted 

 into females; but whether there are any species in a 

 state of nature which co-exist as monoecious and female 

 individuals, I do not know. 



The third Class consists of dioecious species, and the 

 remarks made under the last class with respect to the 

 amount of difference between the male and female 

 flowers are here applicable. It is at present an inex- 



* Delpino, ' Studi sopra uno xi. p. 507, and 1875, p. 26. On 



Lignaggio Anemofilo,' Firenze, proterandrous and proterogynous 



1871. hermaphrodite individuals of the 



t Delpino, ult. Osservazioni same species, see H. Miiller, ' Die 



suUa Dicogamia,' part. ii. fesc. ii. Befruchtung,' &c., pp. 285, 339 



p. 337. Mr. Wetterhan and H. % ' Gardener's Chron.,' 1847, pp. 



Muller on Corylus, Nature,' vol. 541, 558. 



