88 Mr Willis and Mr Bnrhill, On Flora of Willows. [May 15, 1893. 



The roots of the perennials go deeply into the humus, 

 and the question arises as to whether thev can draw from 

 thence, unaided, all the materials required for their growth. 

 Loew thinks this improbable, and suggests that mycorhiza comes 

 into play ; he has observed this on several species. It does not 

 seem to us, however, that this is necessary, considering the age 

 of the humus, much of which must be fully decayed, and considering 

 also the amount of dust which must blow into the bowl-shaped 

 tops of the willows in the course of many years. Hoveler* in a 

 recent paper has shown that plants are able to make use of humus 

 without the aid of mycorhiza. We hope to investigate this point 

 further. 



With reference to water supply, an important question in 

 regard to epiphytic plants, the large masses of humus present in 

 the willow tops must retain a great deal of water, dry though the 

 climate of Cambridge is. The crown of leafy shoots upon the 

 willow tree itself will also protect the " epiphytes " from transpira- 

 tion. We have noticed a tendency to a bulbous enlargement of 

 the base of the stem in one or two specimens of Holcus lanatus 

 and Poa annua. 



To sum up, the one character of epiphytes -f- which is well shown in 

 these plants is a well-marked adaptation of the seeds to distribution. 

 They possess no special methods of clinging to their supports, nor for 

 collecting water or humus, beyond what has been above described. 

 They are, nevertheless, of interest as showing a tendency in the 

 direction of epiphytism. Such an epiphyte as jEschinanthus might 

 perhaps be compared with them. This side of the question is 

 discussed more at length in Loew's paper. 



In conclusion, one or two miscellaneous points may be men- 

 tioned. 



The record of Lactuca muralis is interesting. It is recorded for 

 the same trees in Babington's Flora, and has thus survived, though 

 an annual, for over 3-5 years in these trees. There are no plants 

 of this species now living on the soil within a considerable 

 distance. 



One or two willows examined had put out roots from the 

 crown into their own humus, and some at least of these had grown 

 right through the willow tree to the soil (cf. the case of the roots of 

 the Elder, above). 



* "Ueb. d. Verwerthung d. Humus bei d. Ernahrung der chlorophyllftihrenden 

 Pflanzen," Prings. Jahrb. xxiv. p. 283, 1892. 



t Goebel, " Pflanzenbiologische Schilderungen," i. pp. 153, 161 &c. 



