I 



:> 



364 PROVISIONAL HYPOTHESIS Chap. XXVII, 



r 



stigma, a few seeds of small size were formed. The pollen- 

 grains of Mirabilis are extraordinarily large, and the ovarium 

 contains only a single ovule; and these circumstances led 



a 



m 



par 



Naudm 11 to make the following interesting experiments, 

 flower was fertilised by three grains and succeeded perfectly, 

 twelve flowers were fertilised by two grains, and seventeen 

 flowers by a single grain, and of these one flower alone 

 each lot perfected its seed : and it deserves especial notice that 

 the plants produced by these two seeds never attained their 

 proper dimensions, and bore flowers of remarkably small size. 

 From these facts we clearly see that the quantity of the pecu- 

 liar formative matter which is contained within the spermatozoa 

 and pollen-grains is an all-important element in the act of 

 fertilisation, not only in the full development of the seed, but 

 in the vigour of the plant produced from such seed. ' We 

 see something of the same kind in certain cases of 

 nogenesis, that is, when the male element is wholly excluded 

 for M. Jourdan 12 found that, out of about 58,000 eggs laid by 

 unimpregnated silk-moths, many passed through & their early 

 embryonic stages, showing that they were capable of self- 

 development, but only twenty-nine out of the whole number 

 produced caterpillars. Therefore it is not an improbable view 

 that deficient bulk or quantity in the formative matter, contained 

 within the sexual elements, is the main cause of their not having 

 the capacity of prolonged separate existence and development 

 The belief that it is the function of the spermatozoa to commu- 

 nicate life to the ovule seems a strange one, seeing that the 

 unimpregnated ovule is already alive and continues for a wu - 

 siderable time alive. We shall hereafter see that it is probable 

 that he sexual elements, or possibly only the female element, 

 include certain primordial cells, that is, such as have undergone 



no differentiation, and which are not present in an active state 

 m buds. 



a con- 



Graft-hybrids.-When discussing in the eleventh chapter the 

 curious case of the Cytisus adami, it was shown that, after the tissues 



torn \ N ° U 9 ; elleS Arcl ^e S du Museum,' n As quoted by Sir j Lubbock in 



* P " A '• ' Nat. Hist. Review,' 1862, p. 345. 



