AN OUTLINE OF PIIYTOBIOLOGY. 2l 



Tlie different types of dissemination are as follows : 



1. Vegetative parts provided with hooks may be carried by 

 fur of animals, as in some cactuses, and possibly the stems with 

 their fruits of our galiums, and Polygonum sayittatum may be 

 carried in the same way. Winter buds and other parts of water 

 plants may be carried in mud by the feet of birds as in Eloclea 

 canadensis. 



2. By clinging apparatus of hooks, etc., seeds or fruits 

 may become attached to wool or fur and be carried far, to be 

 finally brushed off or to be shed with them, or spines may be 

 developed which stick into the feet of animals. Mammals, 

 because of their shaggy coats, are best adapted for this mode of 

 dissemination, and accordingly it is common in herbs, and rare 

 in shrubs or trees. Hooks, more or less large and strong, are 

 formed from bracts as in the burdock, from outgrowth of the 

 calyx as in Agrimony, calyx teeth as in Convposito', ovary or 

 part of it as in Desmodium, inferior ovary as in Umhellifera', 

 Circaea, the style as in Polygonum virginianum, the seed itself 

 as in Villarsia nymphaeoides. Hooked fruits are numerous but 

 hooked seeds rare, for in the ovary where many are closely 

 pressed together there is not room for the development of 

 hooks. Spines which project straight from the fruit and stick 

 into the hoof of animals occur in a few plants, and in other 

 cases there are formed many projections arranged in lines so 

 that the fruit clings in wool or hair as a comb does. 



3. A sticky substance is formed which makes fruits or seeds 

 cling to the fur, feathers or feet of animals, a peculiarity partic- 

 ularly common in water-plants. This may be formed either by 

 special glands or simply over the general surface. It may be on 

 the calyx as in Salvia glutinosa and Plumbago, in the ovary as 

 in Linncea horealis, on the seed itself as in Collornia, and rarer 

 cases are known where it occurs upon other parts. In parasites 

 the seeds are usually sticky, but doubtless this is as much to 

 make them cling to branches as to secure locomotion. 



Another very important phase of this subject is the carrying 

 of seeds in the mud which clings to the feet of birds and hoofs 



