McAllister. — Nuclear Division in Tetraspora lubrica. 691 
Oedogonium takes place without visible centrosomes though the spindle 
seems clearly intranuclear. 
The appearance in the antheridia of certain Liverworts \Marchantia 
(22, 58), Fegatella (55), Riccia (30) and others] of centrosome-like bodies in 
the last cell generations before the formation of the motile gametes suggests 
the possibility of centrosomes appearing at or shortly before the stage at 
which the blepharoplast is present. While the three nuclear divisions of the 
vegetative cell of Tetraspora lead to gamete formation and should, on the 
above hypothesis, be especially favourable for the detection of centrosomes, 
nevertheless they show no such bodies. 
According to the literature on mitosis in the Protozoan cell, many 
low forms have the chromatin of the nucleus concentrated in the nucleole. 
Such phenomena have been reported for Hydrodictyon and Sphaeroplea by 
Golenkin (19) and have been expected by some in other genera of the lower 
green Algae. Golenkin’s results are probably to be explained as due to 
improper fixation or staining, since both Timberlake and Yamanouchi have 
demonstrated the presence of a reticulum in Hydrodictyon. Further 
research with Sphaeroplea will probably give similar results. It appears 
then that Spirogyra alone among the green plants thus far investigated is 
still in doubt. If we attempt to explain this divergence of the mitosis in 
Spirogyra on the ground that the Conjugatae probably arose contem- 
poraneously with the Chlorophyceae from a common ancestor, and have 
developed their mode of mitosis independently of the latter group, we are 
confronted with the facts that in Zygnema and Closterium the nuclear 
division is well proved to be similar to that in the higher plants. The great 
uniformity in the nuclear phenomena of the line of green plants beginning 
with the Chlorophyceae leads one to expect a similar uniformity in the 
Conjugatae. According to the literature on this latter group such uni- 
formity does not exist. Contrary to Moll’s suggestion, this lack of 
uniformity probably is to be found in the investigator and his methods 
of fixation and staining, &c., rather than in the different species of Spirogyra. 
This conclusion is borne out by the fact that different investigators interpret 
differently the nuclear phenomena of the same species. For example, Moll 
believes that all of the chromosomes of Spirogyra crassa come from the 
nucleole, while van Wisselingh reports that but two come from the nucleole 
of this same species, while ten arise from the reticulum. 
Dangeard’s suggestion (11) that the groups Chlamydomonadaceae and 
Euglenidae be separated on the basis of their type of nuclear division was 
based upon a comparison of a number of genera of both orders. Although 
objection may be made to the terms ‘ teleomitose ’ and ‘ haplomitose ’ on 
the ground that the latter term implies too great simplicity of mitosis, it 
nevertheless seems clear that two perfectly distinct types of nuclear division 
exist here. In the Chlamydomonadaceae there are no centrosomes and the 
