284 PHYSIOLOGY. BOOK II. 



cal that it really seems to me impossible to say with which the 

 discovery about to be mentioned originated : it will therefore 

 be only justice if the Essays referred to are spoken of collectively, 

 instead of separately. These two distinguished botg,nists as- 

 certained that the production of tails by the grains of the 

 pollen was a phenomenon connected with the action of fer- 

 tilisation ; they confirmed the existence of the suture des- 

 cribed by Ehrenberg ; they found that the true stigma of 

 Asclepiadeae is at the lower part of the discoid head of the 

 style, and so placed as to be within reach of the suture 

 through which the pollen tubes or tails are emitted; they 

 remarked that the latter insinuated themselves below the head 

 of the style, and followed its surface until they reached the 

 stigma, into the tissue of which they buried themselves so 

 perceptibly, that they were enabled to trace them, occasionally, 

 almost into the cavity of the ovarium ; and thus they esta- 

 blished the highly important fact, that this family, which was 

 thought to be one of those in which it was impossible to sup- 

 pose that fertilisation takes place by actual contact between 

 the pollen and the stigma, offers the most beautiful of all 

 examples of the exactness of the theory, that it is at least 

 owing to the projection of pollen- tubes into the substance of 

 the stigma. In the more essential parts these two observers 

 are agreed : they, however, differ in some of the details, as, 

 for instance, in the texture of the part of the style which I 

 have here called stigma, and into which the pollen-tubes are 

 introduced. Brongniart both describes and figures it as 

 much more lax than the other tissue ; while, on the other 

 hand, Brown declares that he has in no case been able to 

 observe " the slightest appearance of secretion, or any differ- 

 ences whatever in texture between that part and the general 

 surface of the stigma" (meaning what I have described as 

 the discoid head of the style). 



It would, therefore, seem that actual contact between the 

 pollen and the stigma is indispensable in all cases. Orchi- 

 deous plants, however, offer an apparent exception; for in 

 them nature has, on the one hand, provided special organs, in 

 the form of the stigmatic gland and the caudicle of the pollen 

 masses, to assist in the act of fertilisation ; and on the other 



