1900] SPOROPHYLLS AND SPORANGIA OF ISOETES 339 
4. The ligule originates in a single vesicular cell as described 
by Hofmeister. The mature ligule can be distinguished into 
four regions: (1) the sheath which has its origin in the lower- 
most cells of the young ligule, (2) the glossopodium, (3) a 
region of living cells, and (4) a region of disintegrating cells. 
5. The rudiment of the sporangium is a transverse row of 
superficial cells below the ligule; the upper part of this gives rise 
to the velum, the lower part to the sporangium proper. 
6. There is no definite hypodermal archesporium. The middle 
cells of the sporangium Av/age are the first to undergo periclinal 
divisions. Additions to the sporogenous complex are made from 
the superficial cells of the sporangium. 
7. The general direction of growth of the sporangium is at 
right angles to the face of the leaf, with a slight tendency in 
young sporangia to an upward direction. The cells are not in 
well-arranged rows or stratified layers. i 
8. There is no evidence that certain of the archesporial cells 
ive rise to trabecule only, and certain others to mother cells 
only. The trabecule and megaspore mother cells or groups of 
microspore mother cells greatly outnumber the archesporial cells. 
9. There is'no evidence that each of the primary cells of the 
Sporangium pursues an independent growth. On the contrary, 
their derivatives blend indistinguishably. 
10. The microsprangia and megasporangia are indistinguish- 
able until they have attained a volume of 15,000-25,000 cells. 
It. The sporangium becomes recognizable as a microspo- 
tangium by its differentiation into irregular deeply-staining and 
feebly-staining radial bands. The deeply-staining regions after 
4 period of active multiplication become the mother cells. The 
feebly -staining regions become the trabecule, walls, and tapetum, 
12. The tapetum is organized out of the layer of sterile cells 
adjacent to the mother cells; its cells are small, densely cyto- 
plasmic, and persistent. 
13. The middle cells of the trabeculae become elongated by 
‘ompression and growth; their nuclei also become elongated 
and spindle-shaped. : 
