Life-History of Isoetes . 251 
Summary. 
The results of the foregoing statements may be briefly 
summed up as follows : 
1. The spores of Isoetes echinospora , var. Brannii , Durieu, 
will germinate as soon as ripe, provided the sporangium is 
artificially opened, but germinate more promptly after a rest 
of several months. 
2. The microspores in germinating produce a single pro- 
thallial cell, and an antheridium composed of four peripheral 
and four central cells, each of the latter giving rise to a single 
multi-ciliate spermatozoid, the body of which is derived from 
the nucleus of the sperm-cell. 
3. The ripe macrospore contains a large elliptical nucleus 
lying in the basal portion. This undergoes division while 
in its original position, but no division-wall is formed. The 
secondary nuclei, by repeated divisions, give rise to a number 
of free nuclei, which lie in the apical region of the future pro- 
thallium, and not until the number is quite large (about 30-50) 
does the process of cell-formation begin. 
4. The process of cell-formation is entirely similar to that in 
the embryo-sac of most spermaphytes. It begins at the apex 
of the spore and proceeds toward the base, following the wall, 
and finally proceeding centripetally, the whole spore becomes 
filled with a continuous tissue. 
5. The first archegonium arises from one of the first 
formed cells, at the centre of the apical region. Its de- 
velopment corresponds closely with that of the Marattiaceae. 
6. Other archegonia (usually two) begin to form before 
the first one is mature, quite independently of its being fer- 
tilized or not. 
7. A small number of secondary archegonia may be 
formed in case the primary ones all fail to be fecundated, 
but the total number is small, not exceeding eight in any 
cases observed. 
8. The prothallium is incapable of independent growth, 
and dies after the supply of food in the spore is exhausted. 
