XIV PKOCEEDIKQS OF THE 



now existing out of their own order. As a postulate tinder the 

 Darwinian theory, we may allow all to have had their origin in a 

 common parent. "We may also, from the scanty evidences supplied 

 by tertiary and cretaceous remains, believe that the parent races of 

 some of our species, or perhaps genera, may have remained imchanged 

 to the present day in company with their modified oifspring. Even of 

 two nearly allied orders one may be more altered from the common 

 stock than the other, and may be thus in a vague sense said to be 

 derived from it and therefore more modern. Thus Cycadese may be 

 supposed to be more ancient than Conifers, Araucarise more ancient 

 than other groups of Conifers ; but the common parent of Conifers, 

 Gnetacese, and other low Dycotyledons belongs to an age so remote 

 as to have left no visible trace to guide us in our conjectures. 



Prom such conjectures, however, as have been indidgedin by phy- 

 logenesists, I gather that the supposed earliest progenitor of the 

 plant-races was a simple organism multiplying by internal growth 

 and division, that at a later stage, besides growth in various direc- 

 tions with a tendency to radiation, sexual elements had arisen, at 

 first, perhaps, without other arrangement than their proximity. From 

 that stage the progress towards the more perfect plant became mul- 

 tifarious, some of the principal courses followed being the differen- 

 tiation of the indefinitely growing axis and its definite appendages — 

 the respective arrangement of the male and female element, of the 

 female at the end of an axis or of one of its branches, and of the 

 male on the appendages — the adaptation of the appendages to the 

 various purposes of vegetation, of protection to the sexual elements, 

 or of assisting them in their functions — the separation of the male 

 from the female element, &c. 1 see no arguments to oppose to these 

 different modes of gradual progress by means of natural selection 

 through a long succession of untold generations ; but they cannot 

 have followed the same sequence in all races of plants. In some 

 the separation of sexes may have long preceded the development of 

 floral envelopes ; in most of the higher Phsenogams the reverse has 

 been the case. Phyllotaxy has become highly developed in several 

 Cryptogams, whilst in some Phaenogams, far advanced as to sexual 

 apparatus, the foliar system has remained in arrear. But in none of 

 these courses have we any evidence of retrogression. We have no 

 more reason to believe that sexes once separated are brought toge- 

 ther again in future generations than that cellular plants should de- 

 scend from those in which the vascular system has been perfected*. 

 * The apparently exceptional case of unisexual flowers, supposed to have de- 



