ON THE STUDY OF ADAPTATION IN PLANTS. 177 



station in the tropics by Dr. Treub. Our European flora 

 is but a small — we may even say, a miserable — fraction of 

 the whole. But it is just that fraction in Botany which 

 has been developed, and thus it happens that our judgment 

 on the organic formation of plants is frequently but one- 

 sided and European. Two examples may serve to illustrate 

 this : among our native ferns, if we except the seedling 

 stage and the scale-leaves of the Osmunda and S truth iop- 

 teris, we only recognise a difference in the development of 

 the leaves to the extent that the form of the sporophylle 

 differs from that of the foliage leaves. Among the tropical 

 ferns some have long been known which, in one and the 

 same specimen, produce leaves of strikingly diverse ap- 

 pearance ; amongst these are a few species of the genus 

 Polypodium (section Drymarid), and the remarkable genus 

 Platycerium. Regarding these' from the standpoint of our 

 knowledge of native ferns it was stated in all descriptions, 

 and, as systematists are usually very conservative, it will 

 probably long be affirmed, that there exists here only a 

 difference between sterile and fertile leaves. My observa- 

 tions made in Ceylon and Java 1 have shown, however, that 

 such is not the case. Sterile and fertile leaves are, on the 

 contrary, formed quite alike in the above-mentioned ferns. 

 But amongst the sterile ones the effects of division of labour 

 become apparent. Most of them are suited, in a manner of 

 which we have no example among our native ferns, for 

 the performance of functions which are connected with the 

 epiphytic mode of life of those ferns just mentioned. Thus 

 Polypodium que re if Hum, Polypodium diversifolium, and 

 others, have leaves which form ledges or pockets upon the 

 stem of the tree on which they grow and in the pockets ; 

 humus formed from fallen leaves, pieces of branches, etc., 

 collects and is absorbed by the roots of the fern, thus 

 enabling- it to attain to its great size. 



Some species of Platycerium possess gigantic pocket- 

 forming leaves, others — such as the frequently cultivated 

 PI alcicorue — form humus by the rapid decay of their 



1 Cf. Goebel, Fflanzenbiologisrhe Schild., 1889-1893. 



