LEAVITT: TRICHOMES OE ROOT. 
297 
Spadiciflorae. 
A list has already been given of the Spadiciflorae in which I have 
found the trichomes to be of the unspecialized type. In two cases 
I have found that the hair-cells are of the second type, viz., in 
a hybrid seedling, Anthurium Andreanum x A. ornatum, and in 
Monstera deliciosa. Figure 70 (plate 18) shows the young tri¬ 
chomes of the root in the latter species. An alternation of hairless 
cells and trichomes with wedge-shaped bases is seen in longisection. 
The base of the trichome often does not reach to the inner plane of 
the layer. In the meristematic tissue the origin of the hair-cells, 
as short, dense wedge-shaped elements alternating regularly with 
longer and less dense cells, was ascertained. The atrichomic cell 
occasionally divides (as is shown in figure 70, plate 18). 
These two cases show the presence in the Spadiciflorae of the 
phenomenon forming the chief topic of this paper. 
Ejstantioblastae. 
Representatives of three families of this group were studied: 
Commelinaceae, Eriocaulaceae, and Xyridaceae. The trichomes are 
of the specialized type. 
Commelinaceae. Of Tradescantia virginica a growing rootlet 
showed trichobiasts as comparatively dense cells, two thirds as 
long as the alternate cells, at a distance of 0.3 mm. from the 
growing poiut, in tissue still covered by the cap. They were 
often lenticular. They had been cut, in the initiatory division, 
from the upper end of the mother cells. The bases of the 
mature trichomes are about one third the length of the 
atrichomic cells. Commelina nudiflora. Figure 71 (plate 18) 
gives in outline an optical longisection of the epidermis of one 
of the transparent rootlets. The first trichoblast appears as a 
proximal segment of the 12th cell from the apex. The divi¬ 
sion wall is straight. The trichoblastic segment is about one 
half as long as its congener. The next older and the remaining 
trichobiasts are rendered conspicuous by the density of their 
contents. Figure 73 (plate 18) shows these bodies in full face 
