64 Proceedings of the Roi/al Irish Academy. 



IV. Artificial crosses between the European and Japanese Larches. The 

 reverse cross, Laric cirropaca ? y. L. Icptolcpis ^ , was artificially made by 

 hand pollination at Murthly in 1914, and 37 cones were produced. These 

 contained a large number of seeds, but only 6 seedlings were raised, which 

 are for so far vigorous in growtli. Twigs sent in 1917, showed one of the 

 seedlings to have yellow twigs like Z. curopaca, while two other seedlings had 

 the reddish twigs of Z. hptohpis. 



The cross, Larir Uplolcpis $ x Z. curopaca J . artiKcially made by hand 

 pollination in the same year, did not result in the production of any seedlings ; 

 but in 1915, wlieu the cross was repeated, three seedlings were raised, which 

 are reported to be not very vigorous. 



It is astonishing how difWcult it is to effect cross-fertilization artificially 

 in the case of niDSt trees, and more especially of conifers. This lack of 

 success is hard to e.\plain. 



The facile production of such hybrids is not possible without much further 

 experimental work. This can only be carried out when the importance of the 

 subject becomes recognized by those in authority. 



Function of Epidermal Papillae. — The remarkable difference in the 

 epidermal cells of the leaves of the European and Japanese larches— the 

 surface of the former smooth, of the latter rougliened with papillae — is no 

 doubt connected wiili the fact well known to foresters, that the Japanese 

 larch bears considerably more shade than the European species. Professor 

 Henry Dixon, K.K.S., has kindly supplied us with the following note on the 

 function of j>iipiIlose epidermal cells : — 



" Haberiandl' consideis that the papillose epidermal cells of leaves act as 

 lenses causing the parallel rays of incident liglu to convei-ge within the cell 

 and fonn a brightly illuminated disc on the screen formed by the protoplasm 

 adhering to the internal surface of tlie back wall of the cell. He supposes 

 that when this disc is centrally placed, as will be the case when the general 

 surface of the leaf is at right angles to the rays of light, no stimulus is 

 emitted for transmission to the motile tissues of the leaf ; if, however, it is 

 displace*! from the central position, a.-? will happen when the incoming light 

 is oblique, a stimulus is perceived by the screen, wliich on transmission to the. 

 motor tissues evolves a response tending to bring the leaf surface perpen- 

 dicular to the light. 



"Whether this theor)- is true or not, it seems to me that a papillose' 

 epidermis must act in another important manner. Much of the light falling 

 upon leaves must strike them either at the augl& of total reflection or of 



' '• Physiological PUnt'Aoatomy," pp. 016-631 (1914). 



