250 THE STRUCTURE OF FLOWERS. 



but male flowers — presumably in consequence of some weak- 

 ness of constitution due to hybridisation. 



It would be quite foreign to my purpose to trace the 

 origin of sexes throughout the vegetable kingdom, as I am 

 solely concerned with that of flowers. But what appears to 

 be pretty certain is that the absorption of the pollen-nucleus 

 by the " egg-cell " involv^es a special form of nutrition, 

 coupled with certain excitant effects. Uuion between nuclei 

 occurs elsewhere ; and as illustrative analogies, one recalls the 

 fact of fusion being normal in the Gonjugatce, and among 

 zoospores, where no sexual differentiations are observable. 

 Again, in the embryo-sac there occurs the union of two nuclei, 

 one from each tetrad, their function being then apparently to 

 form endosperm. As another case, Mr. Gilburt has described 

 the union of the nuclei of cells constituting a " cell-gi'oup," 

 which forms a wood-fibre after the absorjDtion of the septa.* 



Of course one of the most essential properties of the 

 pollen-nucleus is to transmit to the offspring characteristics 

 of the male parent : but even this is paralleled in the vegeta- 

 tive system ; for an engrafted scion can transfer its peculi- 

 arities to the stock, as has occurred with Cytisus Ada-mi, 

 variegated Abutilons, etc. 



If, however, we ask what are the actual differences which 

 exist between the male and female energies, and how they 

 have arisen, we at once find that we are completely baffled, 

 and that all speculations are at present futile. 



* Morph. of Vej. Tiss., Journ. Roy. Micr. Soc, 1879, p. 806 (note). 

 Schacht observed a similar origin of liber-fibres in the Papaw, each of 

 which was originally composed of three or four cells, but the septa 

 become absorbed; their original positions being only indicated by 

 clusters of pores on the walls {Les Laticif. die Carica Papaya, Ann. des 

 Sci. Nat., 4 ser., viii., pi. 8, figs. 9, 10). Treub, on the other hand, dis- 

 covered the laticiferoQS vessels and liber- fibres of the Nettle, etc., to have 

 arisen by repeated division of the nucleus, the partitions not having been 

 formed at all {Arch. Neerl. des Sci. Exac. et Nat, torn, xv., 1880, p. 39). 



