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vascular tissues form, while, later in the season, the space between 
the bark and wood becomes more and more crowded, the cell 
material is all the while subjected to increasing pressure, and the 
tissues formed later spread out in the direction of the circumference 
of the stem, are hence greatly flattened, and the bore so reduced as 
to present a more dense appearance. 
That there are some plants among Exogens that do not present 
a distinct marking, and some that have none whatever, does not 
disturb this general theory of growth. Such cases may be set down 
fairly and properly as unexplained exceptions. On the other hand 
that there are Exogens that do constantly form two or more tubes of 
wood in a year does not refute the theory. I have laid upon the 
table here, this evening, specimens of Exogenous stems which have 
made from five to ten distinct separable rings in one season. The 
Beet has been brought up here as an instance of the formation of 
more than one ring ina year. But the whole order Chenopodiacee, 
with Amarantacee and other allied orders are subject to these 
phenomena, and I think these exceptions are far more numerous than 
is generally supposed. 
What we wish to get at, however, is this: Is it true in general, 
that our Exogens may, and frequently do, form more than one dis- 
tinct tube of wood in one year ? 
If the formation depends upon two conditions, viz : a period of 
activity and one of repose, then it would be logical to infer that a 
ring of wood may be formed, whenever, and as often as, these two 
opposite conditions succeed earch other, and that the rings, or tubes, 
would be more or less sharply distinguishable, as those periods were 
sharp in succession For example: if, after the the middle of July, 
a severe drought should come on, accompanied by much high wind, 
and should prevail till the end of August, and this drought be suc- 
ceeded by a very warm and wet September, I believe. that two dis- 
tinct tubes of wood would be made by most of our Exogens, and 
that these rings would be so sharply aetie: ppranape as to seem like 
two years’ growth 
There are other circumstances generally, present that may make 
two or more markings in one year, not so sharply distinguishable. 
My attention was first drawn to this subject by the examination 
of a potatoe, which had made what the farmers call a second 
rowth. It was after a severe drought had been succeeded by a wet 
season, and potatoes took on a new layer which more than quadru- 
pled the size they had attained previous to the wet period. 
I have examined many stems, and find that the Beet, Cheno- 
podium, Amarantus, Atriplex, and other genera of these and allied 
orders are constant exceptions to the accepted theory. 
‘From my observations I infer that the Magnolia glauca makes 
two or more rings of wood in a year. I have noticed that the Mag- 
nolia puts forth three distinct sets of leaves in one year. The first 
crop appears in May; in the course of about three weeks another 
very distinct crop appears ; the third appearing late in June. In 
the intervals there must be a considerable amount of cell material 
diverted from wood structure to leaf building, and the growth of the 
