536 



Dr. J. C. Willis. On the Lack of 



Hydrdbryum lichenoides: H. olivaceum, Willisia selaginoides, Lawia 

 zeylanica, Dicrcea Wallichii. 

 H. sessile : ? 



H. olivaceum : Lawia zeylanica, Farmeria metzgerioides, Dicrcea stylosa 

 elongata, dichotoma, Hydrobryum lichenoides. 

 H. Griffithii : ? 



Farmeria metzgerioides : Lawia zeylanica, Hydrobryum olivaceum, Podo- 

 stemon subulatus, etc. 

 Farmeria, indica : ? 



When we remember that often a certain species does not grow in the 

 same district as another species, and that these are only a few observations, 

 it is pretty evident that almost any species could live with almost any other, 

 or in almost any place. In Brazil I have found the most incongruous- 

 looking species, such as Tristicha hypnoides and Apinagia Biedelii, or 

 Mniopsis Weddelliana and Mourera aspera, growing side by side, inter- 

 mixed, in two or three localities. Further, in the State of Rio, their habitat 

 is nearly always shared to some extent with a moss, which appears to be 

 able to survive on the dry rock if exposed to the air by the fall of the water. 



As regards other conditions of life, it may be pointed out that these 

 plants escape to a large extent from competition with other plants, for, 

 except for an occasional moss or fern, nothing else is ever found on the 

 rocks with them, and, owing to the enormous destruction of seed before 

 germination, there is little competition among themselves. They are to 

 some considerable extent attacked by such animals as can get at them, for 

 they are very rich in starch towards the end of the season. 



Their conditions of life, then, are in the very highest degree uniform, but 

 in no sense can this be said of their morphological construction, which is the 

 most various and complex that one can conceive. By no stretch of imagina- 

 tion can the variety in the conditions of life be made to fit one quarter of the 

 variety of structure. While the conditions of life and the variations in 

 those conditions are the same in Brazil, India, and Africa, and certain 

 almost identical species occur in all these places, the general trend of the 

 morphological construction in India is towards flattened primary roots, in 

 Brazil towards flattened secondary shoots, and in Africa, so far as our at 

 present extremely limited knowledge goes, sometimes, at any rate, towards 

 flattened roots combined with tall stems. 



Morphological Structure. — Before going further, as these plants are not very 

 familiar to most botanists, it will be well to sum up in brief some of their 

 morphological peculiarities. Taking first the family Tristichaceae (Tristicha, 

 Lawia, and Weddellina), be it noted first of all that the members of this 



