378 Mrs Arber, On Root Development in Stratiotes aloides L. 
V. Summary. 
In the present paper an account is given of certain features 
in the general development and the cytology of the adventitious 
roots of Stratiotes aloides L., which may be briefly summarised as 
follows :— 
A. Anatomical Results. 
(i) The apex of the young adventitious root is clothed ina 
uniform cap of tissue, in which no distinction can be recognised 
between a pericyclic root-cap and an endodermal digestive sac, 
In this respect the results agree with those of D. G. Scott, and are 
opposed to those of Van Tieghem and Douliot. 
(ii) The origin of the lacunz of the middle cortex is shown to 
be due to differences in the rate of growth of the different tissue 
regions of the root. 
B. Cytological Results. 
(i) The nuclei of the young vessels and of the young root 
hairs are shown to be relatively of great size—a feature which 
possibly indicates unusual plasticity in the nuclei of this plant. 
(ii) In the stem and leaf, bilobed nuclei and cells with more 
than one nucleus are shown to occur, but this peculiarity is much 
more important and conspicuous in the young adventitious roots 
where it occurs in the root-cap, cortex and stele. These observa- 
tions have been made upon plants collected in 1910, 1911 and 
1912 from two different localities. It is suggested that amitosis 
supplements karyokinesis in the early development of the adventitious 
roots. The behaviour of the nuclei is considered in relation to 
the life-history of the species, and the paper concludes with a brief 
discussion of the significance of amitosis. 
EXPLANATION OF PLATES. 
Prate VIII. 
Stratiotes aloides L. 
Fig. 1. Semi-diagrammatic sketch of a stem, as it appears in 
August, bisected longitudinally. (v.c. = vascular central region of stem; 
c.=stem cortex; J.t.=leaf trace; /.=leaf; fb. = young stolon; s.= 
squamula intravaginalis ; r. = adventitious root.) (Nat. size.) 
Fig. 2. Tangential section through the middle cortex of a young 
root to show the origin of the lacune (/ac.). (x 318.) 
