* 



408 . MR. F. DARWIN ON SOME GLANDULAR BODIES. 



bearing on Cecropia. I have already expressed the opinion that 

 the food-bodies of this plant aboriginally existed as secreting 

 glands, and that by the retention of the secretion they were deve- 

 loped into food-bodies. Now in the fern we have an intermediate 

 stage, a true secreting gland, which is, at the same time, gnawed. 

 If in this case the secretion were to be retained, the gnawing 

 would be probably continued, and the glands would thus be con- 

 verted into rudimentary food-bodies. 



The existence of the secretion in the fern is also of interest in 

 another way. I believe that the food-bodies of the Bull's-hom 

 Acacia are developed from embryonal glands at the tips of the 

 leaflets. I was convinced that those of Cecropia are likewise homo- 

 logous with glands ; but I was unable to hear of any case in which 

 such structures are situated at the base of a petiole or branch. 

 The fern shows us that a secreting gland may be found in such a 

 situation. In Delpino's paper on Extra-floral Secreting Organs 

 there is no mention of the glands of Pteris Aqailina, nor, indeed, 

 any allusion to the production of a sweet fluid by any cryptoga- 

 mous plant. It is probable therefore that the functional signi- 

 ficance of this organ has not been noticed. In the same paper 

 Delpino states his view that whenever a sweet fluid is secreted 

 elsewhere than in the floral nectaries, it serves as a protection to 

 the plant by attracting ants, which keep other creatures away, just 

 as occurs with the Bull's-horn Acacia, and the Passion-flower 

 mentioned by Mr. Beltf. The fact that the fern secretes a sweet 

 fluid seems strongly opposed to such a view ; for this plant is sin- 

 gularly free from enemies, not being eaten by the larger animals, 

 by rodents, or by grasshoppers. 



In the fern the secretion of a sweet liquid is decidedly connected 

 with the growth of the young fronds ; for it ceases when they are 

 mature. Again, the honey-like fluid on the stipules of Vicia 

 sativa has been shown by my father to be secreted only while the 

 sun shines on them. It appears that, in these cases, the secre- 

 tions are dependent on the continuance of active vital or chemical 

 changes in their immediate neighbourhood. They seem, in fact, 

 to be of the nature of excretions, waste products utilized as food 

 by the ants in the same way that the sweet excretion of the Aphis 

 is made use of by them. 



* Bullettino Entomologico, 1874. 

 t Loc. tit 



