Notes . 
143 
cineae), where the number of cell-generations in the gametophyte is, 
generally speaking, much greater than in the Phanerogams, the ques- 
tion arises, — Does the reduction in the number of nuclear chromosomes 
take place as in the Phanerogams, and if so, does it take place at the 
same stage, or has there been a shifting of the morphological point at 
which this process occurs in the phylogeny of the vegetable kingdom ? 1 
In reply to this question I could say that the details of the karyoki- 
nesis in the spore-mother-cells of these plants correspond exactly to 
those seen in the mother-cells of the pollen. There is the* same 
protraction of the first phases of division, the same thick and ex- 
cessively short chromosomes, and the same early longitudinal division 
of the chromosomes. It will perhaps be asked why the number of 
chromosomes in the two generations was not directly ascertained. 
The answer is that in most of the Muscineae the nuclei are so small 
that the study of the karyokinesis is very difficult; whereas in the 
Pteridophyta, on the other hand, though the nuclei are large enough, 
the number of chromosomes in the forms hitherto examined is so great 
as to make even an approximate determination often almost impossible. 
At the same time, as far as a rough estimate can be of any value, such 
results as were obtained are favourable to the hypothesis that the 
reduction takes place in the spore-mother-cells, and persists through- 
out the gametophyte. I hope, however, to bring this question to 
a definite solution, either by finding more suitable material or by 
improving the methods of research. It will be a matter of great 
morphological as well as physiological interest, to establish beyond the 
possibility of a doubt that the alternation of generations, which is so 
remarkable a feature in the life-history of plants, is dependent on 
a change in the configuration of the idioplasm ; a change, the outward 
and visible sign of which is the difference in the number of the nuclear 
chromosomes in the two generations. 
E. OVERTON, Zurich. 
BOTANICAL NOTES, No. 4.— ON THE VELAMEN OF 
ORCHIDS. — It is a general rule that the roots of terrestrial orchids 
are devoid of a velamen, whilst those of epiphytic members of the 
1 This question was first raised by the writer, at the end of a paper read in 
January 1892 before the Zurich Botanical Society. 
