706 Mr. Brown on the Oi^gous and Mode of 



power of 150. With a power of 300 or 400 indeed, extremely 

 minute and very transparent granular matter may be detected ; 

 but such granules are very different from those which have been 

 supposed to belong to the grains of pollen. 



As an entire pollen mass is usually applied to the surface of 

 the stigma, and as a great proportion of the mass so applied is 

 acted upon by the fluid in which it is immersed, the tubes pro- 

 duced are generally very numerous, and together form a cord 

 which passes through the channel of the stigma or style. 



On reaching the cavity of the ovarium this cord regularly 

 divides into three parts, the divisions being closely applied to 

 those short upper portions of the axes of the valves which are 

 not placentiferous ; and at the point where the placenta com- 

 mences each cord again divides into two branches. These six 

 cords descend along the conducting surfaces already described 

 when speaking of the unimpregnated ovarium, and generally 

 extend as far as the placentae themselves, with which they are 

 thus placed nearly but perhaps not absolutely in contact. 



The cords now described, both general and partial, seem to 

 me to be entirely composed of pollen tubes, certainly without 

 any mixture of the utriculi of the stigma, or, as far as I can 

 ascertain, of the tissue of the conducting surfaces. 



In two cases, namely Ophrijs apifera and Cypripedkim spec- 

 tnbile, I at one time believed I had seen tubes going off laterally 

 from the partial cords towards the placentae and mixing with 

 the ovula ; but I am not at present entirely satisfied with the 

 exactness of these observations, and I have never been able to 

 detect similar ramifications in any other case*. 



That the existence of these tubes in the cavity of the ovarium is 

 essential to fecundation in Orchideae, can hardly be questioned. 

 But the manner in which they operate on, or whether they come 



* See Additional Observations. 



actually 



