24 THE peesident's addkess. 



limitations of adaptation, or point out the danger of assuming 

 that form and structure as we now see them are ad hoc adapta- 

 tions to existing conditions. 



The sundew (Drosera), living, as we know it in this country^ 

 in a substratum almost devoid of nitrogenous food-stuffs, the 

 sponge-like sphagnum-bog, has developed an efficient means 

 for obtaining its nitrogenous food from the bodies of insects,, 

 which it first attracts, then captures and finally digests. In 

 the form and structure of the leaf -tentacle, you, as microscopists,. 

 will appreciate the beauty and apparent perfection of adjust- 

 ment of the details of structure to the end in view. 

 , The genus Drosera, represented in Britain by three species, 

 is a large and widely distributed one. There are about ninety 

 known species ; the British are widely distributed in the 

 northern hemisphere, others are in South- East Asia, South 

 Africa and North and South America ; but the richest area is 

 extra-tropical Australasia, especially West Australia in which 

 occur more than half the known species. The type of habit of 

 our native species, a rosette of basal leaves with a central stem 

 bearing a few flowers, is also widespread. But in South- Western 

 Australia a remarkable secondary adaptation has arisen. A 

 number of species occur with long thread-like stems which 

 climb over low-growing shrubs or bushes, attaching themselves 

 to leaves or twigs by means of the marginal tentacles. You 

 will notice that the climbing leaves are distinguished by their 

 longer stalks; they arise at intervals on the elongating stem, 

 which bears also numerous leaves which still retain their 

 purely insectivorous habit. The specimen shown I collected in 

 a gully on Mt. Lofty, near Adelaide in South Australia. In 

 the same gully were growing large patches of a species with 

 a leaf-rosette recalling our D. rotundifoUa in habit, but with 

 larger leaves and white flowers as big as a buttercup. The 

 South- West Australian species show a great variety in flower- 

 colour, yellow, white, pink, scarlet, crimson or purple, and the 

 plants vary in size from minute forms with leaf -rosettes scarcely 

 more than one inch in diameter, and with flower-scapes little 

 more than an inch high, to sturdy, erect, much-branched plants 

 three feet high or to climbers reaching a length of five feet. 



About two-thirds of the species of Drosera are epigeal — that 

 is to say, do not persist by means of a permanent underground 



