BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 443 



appear to be normally self- fertilizing. Since their flowers Lave no 

 nectaries for attracting insects suitable for effecting fertilization, we 

 can not say that the presence of ants on the surface of the plant tends 

 to drive away apterous insects that might appropriate the nectar without 

 profit to the plant. 



Perhaps the ants might in certain cases assist in transporting the 

 seeds of the plant, which are covered, like those of the mistletoe, with 

 a viscous matter; but such dissemination seems to be effected more 

 commonly by carpophagous birds, who carry them from one tree to 

 another, or by the rain, that washes them from the upper to the lower 

 branches of the same tree. There seems to be no doubt but that the 

 Myrmecodias and the Uydnophtums are derived i'rom Rubiacese that 

 were primitively terrestrial or but feebly epiphytic. Their affinities 

 with Uragoga are very strong. Usually epiphytic plants need for their 

 development a small quantity of vegetable detritus in which their seed 

 can be sheltered while germinating. Normal epiphytes are not pro- 

 vided, as are these Iiubiacea?, with fruits having viscous pulp that 

 causes their seed to adhere to the surface of the bark upon which they 

 fall, and would be unable to gain a lodgment on such a surface. 



These Rubiacea 1 seem, in fact, to be intermediate forms between the 

 normal epiphytes and the parasites, such as the Loranthaceae, whicli 

 are likewise provided with viscous fruits (mistletoe) whose dissemina- 

 tion is effected by fruit-eating birds. The seeds of these Rubiacese are, 

 at the time of their germination, peculiarly situated. Subject to desic- 

 cation, which is very likely to occur upon the surface of the bark, they 

 can not borrow from the tree on which they rest the moisture necessary 

 for their life, as do the plantlets of parasites. They must, therefore, 

 create for themselves a store of water. This is done by the thickening 

 of their hypocotylous axis, which enlarges into a tubercle that acts as a 

 reservoir. 



Beccari supposes that the formation of the flocculent tissue of the 

 tubercle is a consequence of this mode of development combined with 

 alternations of dryness and moisture. But this tissue develops from an 

 internal generating layer, and, since it is composed of dead and dried 

 cells, it seems more logical to suppose that it results from the starvation 

 of such cells because of the formation about them of a corky layer that 

 deprives them of all nutritive material and vascular connection. This 

 would be an example of true parasitism of one tissue in relation to 

 another, the generating layer acting like a parasite as regards the 

 central parenchymatous layer. 



Since Treub has not followed the complete evolution of a Myrmecodia 

 from its germination up to its adult state, we may admit the opinion of 

 Beccari until a formal demonstration of its error shall be furnished. 

 According to this author, though the ants may not at the present time 

 be necessary for the formation of the bulbiform enlargement of the 

 hypocotylous axis, they are required for its future growth. To state 



