168 PHILOSOPHICAL NOTES ON 



resist the tearing force of tides, waves, &c. We see this disk then 

 splitting up into fingers and extension processes as in Fig. 44, for 

 the purpose of a safer grasp of the surface, on which it became 

 attached. It must not be forgotten that any little advantage 

 gained in this way would enable it to remain fixed in a feeding 

 water suitable to its needs, instead of being carried away into deep 

 water by the tide, and be eaten up by herbivorous animals, or 

 otherwise perish. The root disk of Cystophora paniculata 

 (Fig. 44) gives us an idea of the development of roots out of the 

 disk of seaweeds. 



In course of time, ^vith the development of the function of 

 anchorage, there grew up simultaneously a function of suction of 

 water and surrounding materials in solution. This new function 

 of suction helped on the growth of the head of the plant, forming 

 the colony. The growth of the head above ground in land plants 

 needed a parallel growth in the organs of anchorage and suction, 

 the former to counteract the force of wind and storms, and the 

 latter to counteract the transpiration caused by the sun, wind, and 

 hot air, and extend the " grazing field." 



Now, aerial roots of orchids, and other plants, and tendrils of 



weak plants do for them what the extension and lignification of 



underground roots do for most plants. In Vitis pterophora, we 



have tendrils and also aerial roots. The latter, like those of Ficus 



Benghalensis, lengthen almost unbranched till they reach either 



water or moist earth, and then they bud out like ordinary roots. 



Functionally, if not botanically, they are tendrils which do not 



serve the purpose of attachment, but of suction, while the tendrils 



proper are aerial roots, which do not serve the purpose of 



suction, but only of anchorage. 



Many phaenogams now grow on dry land surrounded by air 

 instead of water. Naturally, a large proportion of their nourish- 

 ment is derived, through the roots, from the moisture of the earth, 

 holding in solution mineral and other ingredients, so that in land 

 plants these organs have developed into very important features, 

 while the nourishment of seaweeds may be mainly derived from 

 the circumambient water, holding in solution the ingredients of 

 their tissues, and in contact with their leaves. 



We can understand that, under certain circumstances, the 

 surrounding water might not contain all that the seaweed might 



