AS PROTECTIVE AGAINST RADIATION. 633 



may be added that the leaflets of Lupin are at first clustered 

 together and conduplicate. The Virginian Creeper has its five 

 leaflets at first conduplicate and suberect ; they gradually curve 

 over and spread themselves vertically like a star, not uulike the 

 method adopted by Lupinus pubescens, as described by Mr. 

 Darwin. 



The petiole of tbe "Walnut-leaf (fig. 15 *), on emerging from the 

 bud (the scales of which, like those of the Ash, are petiolar), curves 

 strongly downwards, so that the leaflets, which are conduplicate, 

 stand in a vertical plane. As the basal ones expand they still 

 remain with their surfaces vertical, and it is not until they are 

 approaching maturity that the petiole rises up and the leaflets 

 spread themselves out horizontally. 



Besides vernation, conduplication, and the subsequent vertical 

 position of leaves and leaflets, as calculated to protect them from 

 the evil effects of radiation, hairs and tomentum &c. must not be 

 forgotten as being bad conductors of heat, and therefore very 

 important aids to protect the organs clothed with them. Foliar 

 organs and axes, when young, are often very hairy, silky, or woolly, 

 as the case may be, which in older states become more or less 

 glabrous, either by the hairs becoming more sparsely scattered 

 by epidermal growth, or by vanishing altogether. Similarly the 

 stellate pubescence or woolly clothing, which is not an unfrequent 

 character of the young condition, often disappears as soon as the 

 surfaces thus protected are sufficiently advanced to require such 

 additional aids no longer. As examples may be mentioned the 

 young shoots of Poplar, Apple, Ivy, &c, while the leaves of Colts- 

 foot are at first densely villous, but soon lose the cottony webs 

 from the upper surface as they become adult. 



Conclusion. — The examples given in this paper could, of 

 course, be multiplied indefinitely ; but enough seems to have been 

 stated to justify a belief in the general accuracy of the deduction 

 that vernation, conduplication, the various positions taken up by 

 developing leaves, &c, all conspire to protect them from the evil 

 effects of radiation. 



* In the printing of p. 632 the woodcuts representing Walnut and Labur- 

 num petiole respectively have accidentally been transposed. 



LINN. JOUBN. BOTANY, VOL. XXI. 3 B 



