944 



orifice of the secundine as far as the nucleus ; but the mode of con- 

 nexion with that organ is very difficult to determine, as may be easily 

 supposed when it is understood that the nucleus is a roundish vesicle 

 of about T 4"j;tfi of an inch in length, and that it is immersed nearly 

 that depth in the secundine. After careful and repeated observation, 

 I am of opinion that the extremity of the pollen-tube coalesces with 

 the apex of the nucleus, but does not penetrate it : I have seen seve- 

 ral cases of such connexion where the nucleus has remained uncovered, 

 in consequence of the abnormal suppression of the growth of the 

 primine and secundine, on parts of the same placenta which had the 

 ovules in a normal state. The course of the pollen-tube may be 

 traced with tolerable precision through the highly pellucid coats of 

 the ovule, without dissection ; but as it is always unsafe to depend 

 on appearances until they have been verified by the removal of alj 

 intervening membranes, I have chosen to ascertain every fact by dis- 

 section, when practicable. I object to the expression, "nucleus co- 

 vered by its own cellular coat," regarding, as I do, this cellular coat 

 as an integral portion of the nucleus. The phrase, " embryo-sac had 

 lost its proper cellular coat," also seems to me ambiguous. This cel- 

 lular coat I suppose to be the external membrane of the nucleus, 

 and if so, I consider that it is not obliterated, though it appears to be 

 at length ruptured at the apex by the prolongation of the contained 

 ovoid embryonic body (whether it be embryo or albumen, or both, is not 

 quite clear) to afford egress to the articulated filament. While in its 

 ovoid shape it is less than x^th of an inch in length, with one or 

 two horizontal septa. To detach it at this stage uninjured, it is re- 

 quisite to employ very careful dissection ; but immediately after it has 

 begun to prolong its apex, it can be very easily made to slide up the 

 secundine by gently pressing at its base, proving that the means of 

 egress by that passage are already provided. The production of the 

 confervoid filament is most certainly a normal process, and is easily 

 observable. At the time when it begins to grow, the ovule is about 

 T ^th of an inch in length, having the base of the primine somewhat 

 inflated, leaving a hollow space below the base of the secundine, of 

 about the same length as the secundine, or ^-s-^th of an inch. 



That the " pistillary cords" consist wholly of pollen-tubes with nu- 

 merous abrupt sinuosities, is sufficiently evident; for they can be 

 traced to the pollen-granules, and are absent before fecundation. 



The " minute black atoms " of the nucleus appear to be small 

 granules of starch : they are somewhat larger than active molecules, 

 and have pellucid centres. 



