ECOLOGICAL 179 



sticky pulp adheres to the outside of the bill, the bird wipes it off 

 on a branch. No doubt the seeds of the berries that are swallowed 

 may be voided from the food canal, and there is a Califomian 

 mistletoe that jerks its seed out with explosive violence, but the 

 roundabout distribution effected by the missel-thrush is typical. 



The drying of the gluey threads of the fruit-pulp draws the seed 

 close to the rough surface of the bark and germination begins in the 

 spring or early summer. Out of the seed there grows a minute process 

 which is usually regarded, not as a root, but as a stump of seedhng 

 stem. In any case, it is indifferent to gravity (a-geotropic) and it 

 grows away from light (negatively heliotropic), and it broadens out 

 into a minute attaching disc. From this there grow out two or three 

 cortical roots which spread up and down in the bark. From each of 

 these a sucker sinks through the bark, at right angles to the surface, 

 and continues until it reaches the cambium, where it stops. Nothing 

 more happens that first year. 



In the next season the suckers send outgrowths up and down the 

 cambium just outside the wood, and from the wood they absorb 

 water and salts. They never grow round the branch, which would 

 tend to strangling; they are not embedded by the increase of the 

 wood, for the elongation of the suckers keeps pace with the formation 

 of new wood. It is in the summer of the year after the sprouting that 

 the young mistletoe develops its first pair of leaves, and later on 

 there are branches as well. Moreover, the outgrowths which extend 

 up and down the branches of the host produce buds which emerge 

 on the surface. From these there may arise new mistletoe bushes, 

 fixed to the branch at some distance from the original parasite. It 

 may be noted that the characteristic bushy growth of the mistletoe, 

 spreading out on all sides, is associated with the plant's indifference 

 to the gravitational stimulus; this mode of branching obviously 

 works better than an entirely vertical growth. 



Some of the mistletoes differ in details from the type we have 

 described. Thus in the genus Loranthus attachment is effected by 

 a broad attaching surface, and sometimes by a radiating growth, 

 the "wood-rose" of some Mexican mistletoes. In Loranthus europceus 

 the absorbing outgrowths show at intervals little swellings which 

 suggest secondary reservoirs for the watery sap. At every turn we 

 find what may be interpreted as adaptations. Thus the leathery 

 character of the leaves in the common mistletoe lessens the loss of 

 water by transpiration, and some other species go much further in 

 this xerophytic direction, notably the quite leafless mistletoe found 

 on juniper bushes in some dry Mediterranean regions. In this last 

 case the photosynthesis must be effected by the pale-green twigs. 

 In this connection Neger calls attention to a very interesting instance 

 of "convergence", that is to say, similarity of structure and habit in 

 forms which are not very nearly related. The leafless L. aphyllus 



