26 
FORMATION OF SEEDS, 
.Difference of 
the flow of the 
sap.. 
Different 
place of the 
apira’s. 
Appearance 
the spirals. 
the seed in the root, but the whole of it j so that the heart can 
be taken out and examined, and of course no person, who 
understands the dissection, can doubt its identity. 
With respect to the flow of the sap in the alburnum vessels, 
it is not regular as in tress : but rises at different times, accord- 
ing to the length of period, or number of months the plant 
remains in existence : in some vegetables three rows of albur- 
num are discovered, in others only two ; but in general there 
is, I believe, very little division between them, and the flow is 
pretty constant, and mostly brings the seeds with it j and they 
are to be found at all times. The alburnum appears to be 
formed in the same manner as in trees, by a twisted or curled 
ribbon, which runs up in a vacancy ; but its wood is very 
different, being extremely loose and weak, and very little 
stronger than in its first state of alburnum, and therefore very 
watery ; and it differs also from trees in another particular, 
its sap-vessels being real cylinders, and not vacancies. They 
also vary in the place in which their spiral vessels mount in the 
stem-— in trees they are found in the last few rows of the sap 
vacancies, besides that which forms the wood. But in herba- 
ceous plants they are discovered next the bark : and it was this 
very circumstance that persuaded me,(in the first years of study,) 
that they might be the returning vessels for the sap, as in all 
twining plants, and herbaceous also, there is a set of cylinders 
(perfectly white) which run next the alburnum, and might 
well deceive in this respect : but when I came to dissect them , 
(which I did in innumerable plants) I found that they were 
all spirals confined in their cases j but when taken to pieces, 
and greatly magnified, easily seen to be such. Perhaps cutting 
3 pentandria digynia plant, in an almost decayed state, shews 
them better than any other, because they are then divested of 
the bark which surrounding, conceals them 5 and when the 
rind is taken off, and the cases severed, they remain quite ex- 
posed. In -all these plants they turn round each leaf repeatedly. 
It would appear as if it was to gain for them that space neces- 
sary to make the spirals act well, by having a greater distance 
of wire to contract and dilate in. In the plants just mentioned 
they form a sort of basket-work at the top of each leaf, which 
appears to give great strength to the leaf- stalk in moving to and 
fro. 
As 
