610 DR A. ANSTRUTHER LAWSON ON 
I mention these facts because I believe they have a direct bearing on the series 
of events associated with meiosis. It is a fact of common knowledge that one of 
the main results of nutrition is the production of new cells, and wherever we have 
merismatic activity, v.e. active nuclear divisions, a high state of nutrition prevails. 
Here, in these spore mother cells, we have not only a high state of nutrition—the 
cells themselves being temporary storage organs,—but also merismatic activity. I 
know of no other phase in the life history where this peculiar double function persists. 
I do not mean to imply by this that all storage cells should become merismatic 
because of their high state of nutrition, but I think it safe to imply that all merismatic 
cells—to be actively merismatic—should be well nourished. Now the archesporium 
is without doubt a meristem, and the point I wish to emphasise in this connection 
is that we have here in these cells a much higher state of nutrition than prevails 
in the cells of ordinary somatic meristems. This important physiological aspect of 
meiosis has, in my opinion, not received the attention it deserves. I consider it 
highly suggestive of at least a partial explanation of meiotic phenomena. I shall, 
however, refer to this aspect of the problem under the head of theoretical considera- 
tions after we have examined the changes which occur in the chromatin and which 
accomplish the real act of reduction. 
THE BIVALENT CHROMOSOMES. 
As already pointed out, when the stage represented in fig. 15 has been reached, the 
spireme threads have lost much of their beaded appearance and the longitudinal fission 
is much less evident. ‘The two longitudinal halves (somatic daughter chromosomes) 
appear to lie very much closer to one another. These changes in the granular nature 
of the threads and the approximation of the two longitudinal halves may easily be 
accounted for by the condensation of the chromatin substance as the threads continue 
to shorten and thicken. This condition (fig. 15) closes a period which in all essentials 
compares with the early prophase of an ordinary somatic mitosis, and what follows it 
marks the beginning of the real act of reduction. 
As the longitudinal fission becomes less evident, as shown in fig. 16, there takes place 
an approximation of the spiremes in pairs. The lateral pairing of the chromosomes, 
which are still of great length, is clearly shown in figs. 16,17, and 18. The uniting 
spiremes, which are comparable to split somatic chromosomes, first come to lie parallel 
to one another, as shown in fig. 17, and as they become shorter and thicker the union 
becomes a close and intimate one, as shown in figs. 18 and 19. ‘That the union here is 
a lateral one and not end to end is perfectly obvious. There appears to be some 
difference of opinion as to whether the pairing of chromosomes is brought about para- 
synaptically or telosynaptically. But the observations of RosrnserG (1909), GREGOIRE 
(1910), YamaNoucut (1908), MryaKe (1905), and others, put it beyond much doubt that 
the parasynaptic is of much more general occurrence than the telosynaptic method. 
On this question, however, I am quite in agreement with those who (Diesy, 1910; GATES, 
