I62 
FRANCIS E. LLOYD 
cell wall takes no active part, saying specifically that the plasma lays down 
the secondary wall (mucilage) on its outer external surface. He believes 
that in so stating the case, he agrees with de Bary and not with Wigand.^ 
It has however been shown in the previous pages of this paper that the inner 
portion of the original cell wall is altered into a hydrocellulose at the time 
when mucilage begins to appear. The mucilage arises therefore by hydro- 
lysis of the original cell wall which shows no striking or excessive secondary 
thickening, and not by deposition by the plasma on this wall of additional 
new material, or by the alteration of a thick secondary cell wall, whether 
laid down as cellulose or as bassorin. Neither Walliczek's view, nor that 
stated by de Bary, is therefore correct. 
This account applies equally to the mallows, cacti, Tilia and tragacanth.^ 
The last named I have been able to study only from a fragment of stem 
opportunely included in a fragment of the gum, and from the gum itself. 
In agreement with Mohl and Wigand, I found the lamination of the muci- 
lage, and the included starch. I found also fragments of the original cell 
walls, both of mucilage cells and of non-mucilaginous parenchyma cells. 
The walls of the mucilage cells bear evidence of extensive hydrol^^sis, as 
they are incomplete and show thinned-out edges, while the others, show a 
tearing effect. The protoplasmic utricula with included plastids and starch 
grains are also very easily identifiable. The original cell walls in the gum 
are usually very thin and only partially present,^ and it would seem that in 
addition to hydrolysis of the cell-wall, that of the middle lamellae must 
also have taken place in order to bring about the result seen in gum traga- 
canth, especially in view of the manner of its exudation. This would seem 
to explain the large amount of ''compose pectique," in part pectose, which 
analyses of gum tragacanth have furnished (Giraud, through Tschirch, 
p. 399). Bassorin is described as insoluble in water, and is regarded as 
furnishing only a mechanical suspension as compared with the mucilages 
of cacti, etc. The distinction is hardly justified. It is true that tragacanth 
produces an imperfect solvation, the degree depending on temperature, 
etc., somewhat as in the case of agar-agar, and that in any event there is a 
lack of homogeneity in the dispersion as compared with one of cactus 
mucilage. Somewhat the same sort of difference is found on comparing 
the mucilage of Tilia or Malva with that of Opuntia, the latter yielding a 
It is hardly profitable to consider Wigand's views too seriously, since he evidently con- 
fused the cytology of the mucilage cells of salep {Orchis sp.) with that of the mucilage 
cells of cacti and mallows (p. 149). Indeed his view quoted above was based on the raphide 
cells of salep and immediately applied to the cacti — an obviously impossible comparison. 
^Whether the "gum" of Sterculia sp. is to be included with these is doubtful. But 
the "bassora-gum" studied by Wigand (/. c.) showed without any doubt that, whatever its 
origin, unknown to Wigand, it has the same character as tragacanth. Sterculia gum is 
said not to show lamination (Maiden, T^f^e Tschirch, vol. 2, pt. i, p. 400). 
^ Just what the thickness of the original walls is in tragacanth I am unable to say. 
Judging however from the illustrations available (Tschirch), they show no evidence of 
marked thickening previous to the arising of the mucilage. 
