4 NATIVE BRITISH ORCHIDACE^ 



2. Metaphase. Formation of spindle with chromosomes on equatorial plate. 



3 . Early anaphase. 



4. Anaphase. The chromosome halves have separated, one complete set going 



to each pole, . • ir • ^.i a 



5. Telophase. Each new group of chromosomes is arrangmg itself mto a thread, 



and a cell-wall is appearing between the two groups. 



6. Division into two cells complete. 



In 4 the chromosomes are connected by fine colourless filaments of cytoplasm.^ 

 As to how far the chromosome numbers may prove of service in discriminating 

 between critical species it is perhaps as yet too early to decide. In the Diandr^e the 

 numbers in the species already explored are 8-9, 10, 11, 12, 16 and about 24- As the 

 Diandr^ have only four genera, so extremely alike that they were formerly aU put 

 under Cypripedmrn, there seems to be a hopeful variety of chromosome numbers, in 

 the Monandr^e, however, in the species so far examined, there seems to be much 

 less variation. The foUowing species of the genus Orchis-corhphora, tmarnata, lati- 

 folia, maculata, mascula, morio, Tramsteineri (var. gigas 20), and ustulata all have the 

 same cliromosome number, i o, as also have Anacamptis pyramidaUs, Gyimmdema conopsea 

 and G. odor atis sum, according to Fuchs and Ziegenspeck. ^- The hybrids Orchis 

 incarnata x ktijolia, latifolia x maculata, latijolia x morio and latijoha x pdustris also 

 have 10 chromosomes. This does not look as if chromosome numbers wiU be very 

 helpful in distinguishing between critical species of Orchis, or between such species 

 and their hybrids, or even between the genera Orchis, Anacamptis and Gjmnadema. 



The chromosome numbers for Gymnadenia conopsea are given as 16 by Strasburger, 

 10 by Fuchs and Ziegenspeck, and 8 by Chodat, which seems to indicate difficulty 

 in arriving at the correct numbers, or possibly the occurrence of different numbers 

 in the same species. Similarly Ustera ovata has the chromosome numbers 16, 17, 

 and 18 assigned to it by various authors. 3 



I That is, protoplasm of the cell, as opposed to nucleoplasm, protoplasm of the nucleus. 

 ^ K Hoffmann, ^r^/?'/V///r»7jj-^«Jir/^<7////f/?'?Btfi'a«//fe, Band X, Heft 3, p. 59°- „,i,;n^ ot- 



3 Pro? F. E. Weiss, F.R.S., P.L.S., teUs me that one of his assistants in ^ancheste worUng a 

 the chromosome numbers in Crucifers found that in the common watercress collected from different 

 countries the chromosome number is considerably more variable than in L^istera ovata. 



