ZOOLOGY AND BOTANY, MICllOSCOPY, ETC. 
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floating organ. The spongy parenchyme of the latter is formed by the 
enlargement of the cortical layers, which are already present, but 
consist hitherto of closely packed cells. The medullary cells are 
stellate when young, but afterwards become rounded ; among them are 
crystalliferous cells, which vary greatly in size. 
Tubercles.* — M. A. Seiguette applies the term tubercle to all those 
parts of the plant where an accumulation of reserve-material takes place, 
which is destined to aid in the perpetuation and multiplication of the 
plant. He treats first of tubercles formed by the stem, with few or no 
secondary formations ; and as a good example of this may be instanced 
the case of Stacliys tuherifera. In this plant the tubercles are formed by 
the internodes of the underground stems, and are very variable in size. 
They are white, and at each of the nodes which separate the swollen 
internodes two opposite scales are to be found. Occasionally, in certain 
tubercles, lateral buds give rise to new secondary tubercles, instead of 
a stem, and in a few days the reserve-materials which were in the 
original tubercle are localized in the secondary tubercles. If a trans- 
verse section be made of a tubercle it will be found to have been 
formed by a considerable development of the pith, accompanied by a 
relatively less augmentation of the cortex. The author compares 
Stacliys jpalastris with S. tuherifera, and indicates many points of re- 
semblance between these two plants. 
In Oxalis cornuta the tubercles are produced by a development of 
the primary tissues of the cortex, pericycle, and pith. The reserve- 
material accumulated in the tubercle was found to consist of starch and 
glucose, with a small quantity of saccharose. In Begonia we find an 
external morphology closely resembling Cyclamen eurojpseum. The 
tubercle of Cyperus esculentus, which is formed by the swelling of a 
large number of internodes, has a very complex structure, the material 
for the nourishment of the plant being accumulated in the greatly 
augmented cortex and pith. 
The author then describes four cases in which tubercles are formed 
on the stem with the development of secondary formations. In Apios 
tuberosa the tubercle is constituted from the non-lignified elements of the 
wood, the exterior elements preserving their function of conduction, 
while the interior elements are transformed into reserve-tissue. 
Tubercles which are formed by the roots may be classed into two 
groups, depending on the amount of secondary formation. In the first 
group, where there is little or no secondary formation, the tuberiza- 
tion is produced by a large development of the cortex and pith 
{Banunculus asiaticus, Asphodelus alhus, Asparagus officinalis, &c.). In 
the second group, where the secondary formations are much developed, 
nearly all the tuberization consists of secondary parenchyme (^Spireea 
Filipendula, Campanula barhata, Lathyrus tuberosus, &e.). 
In Bryonia dioica the tubercles are formed by the swelling of the 
underground stem, and towards their base by the swelling of the root. 
In a transverse section of the upper part of a young tubercle, four 
primary woody bundles will usually be found arranged in a single circle. 
* Rev. Gen. dc But. (Bonnier), i. (1889) pp. 415-29, 471-8G, 509-3G, 558-81, 
611-29 (115 figs.). 
