430 Robertson . — The ‘ Droppers 3 of Tulipa and Erythronium. 
long. Tristan 1 mentions that stalked bulblets occur in Allium vincale. 
Some Snowdrops ( Galanthus nivalis ), sent me by Mr. Aveling Green, show 
a similar adaptation in a very striking fashion. In Galanthus the growth 
is monopodial, the flower being produced laterally, and in these specimens 
the axis had elongated greatly, carrying the new bulb some little distance 
from the parent (e. g. Fig. i). Mr. Aveling Green tells me that ‘where 
they have been growing for some years in a mass, the under ones have tried 
to get along under the mass, and to find a way up and form a second bulb. 5 
I have also seen exactly the same elongation of the axis in a specimen of 
the Snowflake (Leucojum aestivum), by which the new bulb was carried 
upwards until its base was 5-5 centimetres above the base of the parent 
bulb. After examining it, I came across a figure and description by 
Irmisch 2 of a precisely similar case in another species, L. vernum. 
(b) Descent . 
To each perennial plant a certain definite depth in the soil appears to 
be specially appropriate, and if it is disturbed it makes efforts to return to 
this particular level 3 . Massart 4 records a most interesting series of culture 
experiments on about 200 perennial species, which were planted, some at 
the normal level, some too deep, and some too shallow. The plants were 
very successful in bringing back their winter buds to the normal level by 
curvature of rhizomes, elongation of internodes, and so on. 
To bulbous and tuberous plants a certain depth in the soil must be 
even more important than to ordinary perennial species, since they want 
protection for their succulent tissues from animals and from frost. The 
need for descent into the soil is especially urgent in the case of the seedling, 
since here the young plant starts at the surface of the ground instead of at 
the level of the parent bulb or corm. The commonest method of descent 
into the soil is by means of contractile roots 3 , which are shown specially 
well in the Crocus. Here, as each successive daughter corm is formed 
above the parent, the need for descent is particularly obvious. The 
contractile root is ‘ always present in the young seedling, and occasionally 
reproduced in after years. ... I fancy I have noticed it to be found more 
frequently in old Crocus bulbs when they have been brought near the 
surface in the process of digging a bed/ 5 The contractile roots of S cilia 
1 M. de Tristan, Histoire des developpemens de quelques gemmes bulbiferes, M&n. du 
Mus. d’Hist. Nat., 1823, T. x, p. 51. 
2 M. Irmisch, Zur Morphologie der monokotylischen Knollen und Zwiebelgewachse, Berlin, 
1850, p. 101, and PI. VII, Figs. 10, 11, 12. 
a F. W. Oliver, The Depth in the Soil at which Plants Occur, Jr. Roy. Hort. Soc., April, 
1898, vol. xxi, p. 486. 
4 J. Massart, Comment les plantes vivaces maintiennent leur niveau souterrain, Bull, de la 
Soc. Roy. de Bot. de Beige, T. xli, 1902-3. 
5 C. Wolley Dod, Gardeners’ Chronicle, 1886, p. 626. 
