224 PROFESSOR ALEXANDER DICKSON ON THE EMBRYOGENY OF 
the seed and form the raphe, runs downwards closely along the course of said 
bundle the whole length of the placenta. To the first mentioned thicker root- 
like process I have applied the term “ extra-seminal root;” to the latter and 
slenderer one, that of ‘placental root.” In applying the term “‘7oot” to these 
processes I do not mean to imply a homology with roots proper. They are 
wholly cellular in structure, and are destitute of the caps so distinctive of root- 
organs; but functionally they probably correspond to roots, which they certainly 
resemble in general appearance. 
In 1863 I submitted to the Botanical Society of Edinburgh my “ Observations 
on the Embryogeny of Tropwolum majus,” in which I confirmed the statements 
of the late Mr Witson, the distinguished author of the “ Bryologia Britannica,” 
as regards the course of the extra-seminal and placental processes, the latter of 
which he was the first to describe in 1843.* I also pointed out (as I then 
believed for the first time) that these processes are developed as lateral out- 
srowths from an originally bottle-shaped germ, in opposition to SCHLEIDEN, who 
had described the suspensor with embryo as originating as a lateral branch from 
an oblong body whose apex corresponded to the extremity of the extra-seminal 
process. At that time I was ignorant of the observations of HormeEIsTEr (1849) 
and of ScuacuT (1855) on this subject. Both these authors had distinctly 
indicated the originally bottle-shaped germ with pointed base.t As to the 
placental process HoFMEISTER makes no mention of it, while Scuacur falls into 
the most extraordinary error regarding it, describing it as passing out of the 
seed through the endostome, and making its way towards the canal of the style{; 
the fact being (as originally stated by Witson, and confirmed by myself) that 
this process makes its way at once through the tissue of the funiculus to the 
placental vascular bundle, along which it runs down in a course directly away 
from instead of towards the canal of the style. 
In his paper Witson described and figured an abnormality, where the extra- 
seminal process, instead of extending itself free in the cavity of the seed-vessel, 
penetrated by its extremity for a short distance into the tissue of the carpel, at 
a point corresponding in position to the chalazal or lower end of the seed. I 
have myself been fortunate enough to detect a precisely similar case, which I 
have represented in Plate XVI. fig. 23, along with a photo-lithographic repro- 
duction of Witson’s figure for the purpose of comparison (Plate XVI. fig. 24). 
Such a deviation seems, at first sight, a triflmg one; but, as the sequel of this 
paper will show, it is of great interest and significance, adding another to the 
* W. Witsoy, “On the Embryo of Tropceolum majus,” London Journal of Botany, vol. ii. p. 623. 
+ Hormeistsr, “Die Entstehung des Embryo,” Leipzig, 1849; Scuacut, “ Ueber die Entstehung 
des Keimes von Tropceoluim majus, Bot. Zeitung,” 1855, p. 641 (translated in “Ann. des Sc. Nat.” 4° 
sér. iv. p. 47). In Plate XV. fig. 18, I have given sketches, A after Hormuistsr, B and C after ScHAcHT, 
showing the earlier stages of this germ. , 
t ScHacut, /.c. pp. 644-5. 


