The Production of Hairs on the Stems and Petioles 
of Tropaeolum peregrinum, L. 
BY 
ARTHUR W. HILL, F.L.S. 
With Plate LVI and seven Figures in the Text. 
T HE common Canary-creeper or ‘ Canariensis ’ 1 of gardens is generally 
assumed to be a typically glabrous plant, and an examination of speci- 
mens grown in the British Isles or of material collected in South America 
preserved in herbaria fully bears out this assumption. Occasionally, however, 
it may be noticed that plants growing under favourable conditions show 
a very few hairs on young stems or petioles, but where they are growing 
normally and luxuriantly no traces of hairs can be seen, and the plants 
are absolutely glabrous. 
In the summer of 1910, 1 noticed that some small plants of Tropaeolum 
peregrmum , growing in my garden, which had received injury to the leaf 
laminae, had developed a few hairs, and from this observation it seemed de- 
sirable to try and find out the cause of the production of hairs, and to 
ascertain the conditions under which it may be artificially induced. In the 
first case in which hairiness was noticed, snails were found to have eaten the 
laminae of the leaves more or less completely, leaving the young plants with 
only stems and bare petioles. 
When making experiments the laminae were removed from healthy 
plants, and after an interval of a few days hairs were quite conspicuously 
developed on the young portions of the stem and on the young petioles. 
Experiments have been repeated during the past summer with greater care. 
Seedlings were grown until they had developed about ten leaves, and all the 
laminae were then removed ; as each new leaf began to develop, its lamina 
was also removed, so that, except for the green stems and petioles, the plants 
were deprived of their main organs for assimilation and transpiration. Some 
of these plants so mutilated have been grown in the open, and some under 
a bell -jar in a moist atmosphere. It was found in August last (Aug. 19) 
that such plants developed hairs in the open in about four or five days, but 
1 Tropaeolum canariense , Hort. T. aduncum , Sm. = T. peregrinum , L. 
[Annals of Botany, Vol. XXVI. No. CII. April, 1912.] 
