TETRAD AND EMBRYO-sAC MITOSES 87 
In the light of the discovery of the fact that true tetrad mitoses 
do not occur in parthenogenetically reproduced plants * we are 
more than ever forced to insist upon the conclusions stated pre- 
viously, that, in such plants as certain Liliaceae, the condition 
must not be interpreted as a suspension of spore formation, but as 
a reduction in the ontogeny of the gametophyte correlated with a 
loss of the spore function, without a loss of the morphological | 
character of the spores so far as their development, as indicated 
by their mitoses, is concerned. The failure of true tetrad divi- 
sions in Alchemil'a and Antennaria is a notable exception which 
proves the rule. : 
The peculiarities characteristic of the tetrad divisions are now 
known to occur in so many plants that we may well pause to esti- 
mate their morphological significance, apart from the relation they 
hold to the maintenance of a constant number of chromosomes. 
In general acceptation the term archesporium has signified a 
cell or cell aggregate from which the spore mother-cells are de- 
veloped, as first defined by Goebel. t . 
These cells cannot, however, be distinguished from vegetative 
cells except by the fact that they are richer in food and plasmic 
content—they have the character of embryonic cells. According 
to their period of growth and the number of divisions they undergo 
their derivatives, the spore mother-cells (taken collectiveiy the 
sporogenous tissue), are few or many. Now the cells of the spor- 
ogenous tissue are different from all other cells in the life cycle 
in that they always suffer tetrad division, and thereby exhibit very 
constant morphological characters which raise them to special 
morphological rank. This cell, or tissue, as the case may be, by 
virtue of the special character attaching to it, demands special 
recognition in terminology, and it would seem both natural and 
justifiable to regard it as constituting the archesporium. The use 
of the term in this way seems to me simple and unmistakable. 
6. Thethird and following divisions are typical, and the reduced 
number of chromosomes is preserved. 
In Crucianella all of the four megaspores in a given series may 
* Juel (7. c.) interprets the phenomenon in Antennaria alpina as a special case 
of apogamy. 
f Bot. Zeit. 38: 545, 56%. 1880; 39: 681, 697, 713. 1881. 
