ON THE FERTILIZATION 



„„^ thousands of pollen-grains with it in 



T 1^ a^l- n.ost methodically and economically d.stnbuted, for unless each 

 ~ £1 onlv allowed to appropriate a single grain, the amount mtroduced would 



ma were 



| ho occurrence 



waji 



inate 



in 



havo to bo indefinitely multiplied. 



,mV ° G f ordinary pollination thus appears to be impossible, and the only 



wl h" a sufficient number of pollen-tubes could be reasonably supposed to ori- 



ould he by means of peculiarities in their development, the primary tubes 



ZriDK from the grains having a capacity for indefinite growth and ramification, 



*« to rivo riso to mycelioid expansions from which branches might be distributed 



■ 



be individual stigmata. There is, however, no evidence of the actual occurrence 



a „y such phenomenon. There is nothing to show that the tubes, whether deve- 



,ped within tho receptacular cavities or as the result of artificial cultivations in 



ui table media, have any special tendency to branch, far less that they have any capa- 



f ( indefinite mycelioid extension. 



The most inn nrtaat evidence against the occurrence of pollination of any sort as a 

 1 at I essential event lies, however, in the fact that the embryo originates, as it does 

 undoubted cases of development, apart from pollination. The embryo, as a rule — for 

 f c< :rse it U possible that pollination and normal evolution may occur in certain indivi- 

 lual flowers -< rtainly arises as an outgrowth of the nucellar parenchyma outside the 



• 



i 



in 



n 





ic and not as the result of special evolution of auy elements contained within 



the latter The embryo-sac up to the period of insect-access and of initial development 



the embryo normally retains the characters of a simple, uninucleate cell. There is 



n. evidence of the formation of an oosphere, of synergidse, or of antipodal cells within 



it, and it is only subsequent to commencing evolution of the embryo that the primary 

 nucleus is replaced by a large number of secondary ones which are apparently related 



to the elaboration of food material for the growing embryo when it gains access to 

 the cavit\ f tho sac. 



Bat if this be so, if pollination be unnecessary, why should the access of insects be 

 Btntial to he development of embryos? The phenomena presenting themselves in 

 nnection with the male flowers of gall-receptacles appear to afford a clue to answering 



his quest m. It is just as impossible for the male flowers to come to perfection— just 

 as impossible for perfect pollen-grains to be developed without the access of insects to 



ho gall-receptacles— as it is for embryos to be developed in female ones under parallel 

 ircumstanc< In the case of the male flowers, however, it is clear that the introduction 



, ^ V¥ ,W^X, 



pollen into the receptacular cavity cannot be the essential determinant of development, 

 bat that this must be related to something else connected with the access of the insects. 

 It iot anythii • directly introduced by the insects that determines the perfect evolution 



the male flower but it is due to effects which their entrance produces on the recep- 

 taele that the evolution becomes possible. The result of the access of the insects, of the 



>ui »re of the gall-flowers and deposition of ova in the interior of the nucelli, is the 



nduction of great irritative stimulation to the activities of all the tissues of the receptacle. 



lhe entire mass of the receptacular tissues undergoes hypertrophic changes similar to 



those occurring in the development of any common gall-growth, and connected with their 



occurren, i an enormously increased flow of sap to the receptacle takes place, as indicated 



the accumulation of fluid under high pressure within the receptacular cavity, and 

 be abundant escape of latex on division of the peduncle or incision of the surface. 



