250 THE LIFE OF THE PLANT 



his aim. Let us remember this conclusion, which will 

 later on prove to be the key to the explanation of 

 phenomena taking place in Nature. 



Let us sum up what we have learnt in this lecture. 

 There is a law underlying organic Nature according to 

 which the cell though able to produce such giants as 

 the Wellingtonia and the Baobab, the age of which is 

 reckoned by thousands of years, is yet unable to reproduce 

 itself endlessly in the same vegetative way. The main- 

 tenance of vegetable forms requires that they should 

 occasionally be renewed by the union of two separate 

 cells. The significance, meaning, and necessity of this 

 law of the existence of two sexes is quite obscure ; it is 

 only an empirical law, based upon the conjoint testimony 

 of all the facts known to us.^ It may be that we are 

 entitled to see in this law only one of the many manifesta- 

 tions of a more general law — the law of the utility of the 

 physiological division of labour, which expresses itself 

 in the fact that the functions fulfilled in the simplest 

 organisms by a single cell distribute themselves over 

 different cells as the organism increases in complexity. 

 The cell may be unable to reproduce itself successfully in 

 all its parts in a long series of generations, and perhaps 

 this labour is divided between two cells, each of which 

 works out only a certain part of the future organism, and 

 taken by itself may be even incapable of further develop- 

 ment. But wherein does the difference lie between these 

 two cells ? Which is the element of development each 

 of them contributes ? These problems are the problems 



' It is worth mentioning that certain seaweeds present a curious instEuace 

 of the sexual process taking place between three cells instead of two, a 

 phenomenon which has no analogy in the rest of organic nature. One 

 of these three cells, being the element fertihsed by the second cell, is at the 

 same time the fertilising element of the third. This fact, quite authentic 

 although unique, together with the fact of the absence of any sex what- 

 ever in the simplest organisms, prevents us from too broad generalisations, 

 from metaphysical theories concerning the existence of a certain organic 

 polarity, and so on. 



