438 Robertson . — The ‘ Droppers' of Tulip a and Erythronium. 
V. Gagea ‘Droppers.’ 
The droppers of Gagea arvensis are figured by Irmisch 1 . They recall 
those of Ttriipa and Erythronium , but are exceedingly short, so that the 
new bulb is carried a very little distance down into the ground. 
VI. Summary. 
The power of lateral migration to prevent overcrowding, and of descent 
into the soil for protection against frost, drought, and animals, is possessed 
in some degree by many bulbous plants. The most specialized methods of 
downward migration are those of certain ‘ tunicate 5 bulbs, Scilla , Gagea , 
Tulip a, and 1 Erythronium. The last three produce the structures known as 
‘ droppers.’ In Tulip a and Erythronium, with which we have been par- 
ticularly concerned in this paper, the immature bulb each year produces 
a single foliage leaf continued at the base into a hollow tube, the ‘ dropper,’ 
enclosing a bulb at its tip. Irmisch’s interpretation of this as partly axial 
and partly foliar is borne out by its anatomy. The region of greatest 
growth in the dropper is immediately behind the apex, showing that this 
foliar-axial organ has become root-like in more than mere externals. Both 
immature and flowering Tulips may produce droppers from lateral buds. 
Tulipa and Erythronium are much alike in almost every point, including 
the structure of the bulb and the external morphology of the seedling, and 
they are regarded by systematists as closely related, but the type of seed- 
ling anatomy in the two genera is curiously different. Tulipa conforms 
to the normal Tulipeae type, while Erythronium is aberrant. In the latter 
genus there are at least three bundles in the cotyledon, and this is correlated 
with a triarch root, while Tulipa has only two bundles in the cotyledon 
together corresponding to the midrib of Erythronium , and a diarch root. 
The triarchy of the Erythronium main root may possibly be connected 
with the fact that the plant depends on it alone for some time, whereas in 
Tulipa a second root is produced almost immediately. 
Note. Since the above paper was written my attention has been 
called to an important treatise in Danish by Christian Raunkiaer, e De 
Danske Blomsterplanters Naturhistorie,’ Bd. I, Copenhagen, 1895-9. The 
author figures and describes external views and dissections of immature 
dropper-bearing plants of Tulipa sylvestris . He also figures a case of 
elongation of the axis in a bulb of Galanthus nivalis (Fig. 104 f) similar to 
that shown in my Fig. 1. He further describes and figures the peculiarities 
of bulb formation in a number of species of Gagea. 
September 17, 1906. 
1 Th. Irmisch, loc. cit., 1850, PI, IV, Figs. 22, &c, 
