122 
Osborne^ on the Wheat Plant. 
these tubes. By tearing out the bars they come away in a 
ribbon of fibre^ spiral_, but yet such a spiral as would result 
from the twisting wire tightly round the surface of a 
pentagonal block of metal, and then unwinding it so as to 
partially release it from the form into which it had been thus 
forced. 
The annular vessels — those in which distinct rings are 
seen — are formed upon a similar principle, but in this case 
the cell-wall is first pitted and afterwards perforated in true 
lines, and thus it becomes eventually cut up into ring upon 
ring ; these are with ease separated, and are seen to be also 
pentagonal. Thus, from a mere dotted or pitted texture on 
the walls of the true cells, is produced ; first the scalariform 
character, and this, according as the direction of the pits may 
be, assumes, when they run into each other, the spiral or 
angular form. 
If one of these tubes is split up, or cut vertically, at that 
stage when the perforations are complete, the edges of the 
divided structure present a series of squared projections, with 
clear spaces between them. 
With regard to the spiral fibre found at the very earliest 
stage of vegetable growth in the plumule, I cannot trace its 
formation ; it seems to come to maturity simultaneously with 
the earliest growth of the vegetable substance in which it is 
seen, not being subjected to the same pressure as that I have 
described above, which grows more gradually, and is bound 
up in a mass of other cell-structure which has grown in ad- 
vance of it ; it does not assume the pentagonal form. I can 
form no theory as to its production ; I cannot find it in the 
seed, but I find it complete at the earliest stage in which I 
can dissect any of the substance protruded. 
I cannot discover any exterior wall or membrane enveloping 
these formations ; I believe them to hold their position by 
being built in by the surrounding cell-texture of the plant ; 
in the roots of plants they are themselves an external pro- 
tection to the sap-tubes I ever find in the bundle formed by 
them. I have made several preparations of vascular tissue 
of the most eccentric form, such as I cannot resolve into 
either annular or spiral, I am inclined to believe that these 
are often the result of the pressure of the covering glass, I 
have never yet been able to trace any visible contents in any 
of these vessels. 
