454 THE GENUS ISOETES IN NORTH AMERICA. 
The TRUNK is generally depressed, broader than high, or flatter in some species (J. Engelmann), 
and thicker and more globose in others (J. melanopoda), but its form is not constant; it is concave 
on the upper side and even somewhat funnel-shaped where the leaves are inserted, while the under 
side shows in almost all the N. American species two grooves and in many exotic ones three grooves, 
dividing the trunk more or less deeply into two or into three lobes. The number of lobes rarely 
varies, so that among the many hundreds and even thousands of American specimens which have 
passed through my hands, I have found only a single, normally bilobed, one with three 
lobes; this was an J. riparia from Philadelphia. In the 3-lobed species the transverse [864 (7)] 
section is rather circular, but in the 2-lobed ones it is usually oblong or often somewhat 
rectangular, narrower in the direction of the grooves and wider in the opposite direction; the verti- 
cal section of the trunk shows a thickness of from 1 to 6 lines, and the transverse diameter a width 
of a few lines to more than one inch. In the centre of the trunk we find a small ligneous body, 
fibres from which enter the leaves and the roots. The mass of the trunk is a white parenchymatous 
or rather cortical tissue, the cells of which are filled with starch. The growth proceeds from the 
central ligneous body outwardly in two or three directions, corresponding to the two or three lobes, 
so that these lobes would spread laterally if their enlargement were not limited by the decay of the 
older (the preceding year’s ?) parts. We thus find that at the period of the most vigorous growt 
about the beginning of fructification, the extreme lateral portion of the lobes becomes discolored, 
brownish, atrophied, and at last black, and is separated from the living tissues by a distinct line of 
demarcation, and at last generally falls off at the end of this or the beginning of the next season as a 
black mould-like mass. In some species, e. g. Z. dacustris, and in colder climates the atrophied cor- 
tical parts continue to cohere for several seasons, and in the Mediterranean J. Hystrix they do not 
seem ever to be detached, so that the trunk of this species reaches a larger size than any other. 
The decaying portions are pushed obliquely upwards when the base of the trunk grows faster 
than the upper part (often in LZ. Zngelmanni, and niuch more so in the Australian J. tripus), or hori- 
zontally outward (the ordinary case), or downward when the upper or leaf-bearing part expands 
more than the lower, root-bearing part. This last is the case in J. Hystrix, where the dead parts are 
turned downwards. 
As the growth of the trunk takes place from the centre outward, the roots, originating from the 
youngest parts, start from the groove itself; and fresh and living whitish ones are only found in or 
near this groove: as they get older they are pushed to the sides, and finally die, becoming brown 
and black. The mass of roots found on Jsoétes specimens are mostly the entangled dead fibres, which, 
by the way, often conceal spores of the previous year, and therefore must be carefully ex- 
amined when no fresh spores are attainable. The root-fibres, sometimes longer than the [365 (8)] 
leaves, are always dichotomously, and often many times, branched. —The upper, concave 
surface of the trunk bears the leaves, the innermost or youngest ones often yet immersed in the trunk. 
The LEAVES are subulate or sometimes almost filiform tubular organs from a broad membrana- 
ceous sheathing base, mostly more or less quadrangular (broader and with sharper edges on the 
upper or ventral, narrower on the dorsal side), or in our terrestrial species more triangular and 
keeled on the back. Their sheathing bases form the bulb, which can be compared to the bulb of 
liliaceous plants ; in fertile specimens it is always larger and thicker than the trunk, and in some of 
the larger ones, e. g. I. Engelmanni and I. melanopoda, attains a diameter of one or two inches. The 
leaves above this ae contain four longitudinal air cavities, lacunae, separated from one another by 
two dissepiments, a transverse and a median one, and irregularly divided by very thin transverse 
septa. The dissepiments are of different, pretty constant thickness in the different species, thinnest 
probably aa ys ony of some injury ; I myself have seen Isoétes with lateral shoots in place of spore-cases. Bot. 
a pasar Be 2 of 1 Tuckermani with four distinct bunches of Zeitung, 1879, No. 1. 
from a single trunk. K. Goebel found a proliferous 
