23 
Pollen Mother-cells of Certain Plants. 
was placed upon the appearance at that time. I have since become con- 
vinced that these prochromosomes are severally arranged in pairs in somatic 
cells of Thalictrum purpurascens. This association of the chromosomes in 
pairs might be expected to lead to the formation of apparent tetrads during 
the prophases of division, which cannot, of course, be associated in any way 
with a reduction process such as is found in the germ cells. Moore and 
Miss Embleton (’ 06 ) have also described the presence of double rods in both 
somatic and pre-meiotic nuclei of Triton , and Farmer and Moore (’ 05 ) have 
described a similar condition in Periplaneta . 
Strasburger (’ 05 ) also found that the chromosomes of Galtonia and 
Funkia , in which they are of different sizes, became arranged in homo- 
logous pairs during the prophases of the divisions in nuclei of embryonic 
regions. He (’ 07 ) has also reported a similar condition for the root-tips of 
Pisum sativum. Strasburger maintains that the parental chromosomes 
mingle, becoming closely associated but retaining their individuality in 
somatic cells, first becoming intimately associated or united in the germ cells 
during synapsis. Just how early and in what manner this intimate 
association occurs remains unsettled. 
Since the pairs are so very closely associated, each pair often appears 
as a single body in both somatic and germ nuclei, which may easily lead to 
mistakes in counting. I find that in my previous counting I mistook the 
pairs of chromosomes for a single chromosome. Therefore the number of 
chromosomes both in somatic and germ nuclei should be twice as many as 
formerly stated. The reduced number of chromosomes in Thalictrum 
purpurascens is 24, instead of 12 as stated by Strasburger (’ 04 ) and myself 
(’ 04 , ’ 05 ). In certain other species of Thalictrum, as Thalictrum minus , 
which is not apogamous, the reduced number is 12. In young pollen 
mother-cells the nuclei have the appearance shown in Figs. 2, 3, 4, and 5, 
PL I. With ordinary magnification the prochromosomes often appear as 
24 single, distinct bodies (Fig. 2, PI. I), while with higher powers (Figs. 
3 and 5, PI. I) each prochromosome appears double, so that each of the 
apparently single bodies is composed of two, or 48 in all. 
Faint linin threads, which are parallel, connect the different pairs of 
prochromosomes, so that the nucleus appears to have two separate and 
distinct spirems, each being composed of a series of prochromosomes with 
intervening linin segments. The nucleus at this period, therefore, has some- 
what the appearance of a post-synaptic nucleus, in which the two component 
parts of the double spirem are more or less distinct. The linin portions of 
these parallel pre-synaptic spirems stain blue with the triple stain. Sometimes 
the prochromosomes appear slightly granular at this stage, and these 
granules may be somewhat distributed or spread out in the linin. The 
structure of this nucleus is, therefore, neither that of a reticulated chromatic 
substance, nor does it have a linin reticulum with chromatic granules evenly 
