THE GENUS EQUISETUM 



undergone. Some of this enlargement is reversible and would have disappeared had the 

 specimen been successfully transferred to balsam, but it unfortunately became detached 

 and was lost in the attempt, and a second photograph more comparable to the other 

 could not therefore be taken. 



The numerical evidence from these and other preparations is as follows. All the 

 species of Equisetum examined have the same chromosome number to a very close 

 approximation. This falls certainly between the limits of io6 and 112, the haploid 

 chromosome number being quoted. It is probable, indeed almost certain, that the 

 chromosome number of all of them is actually 108. 



Fig. 220. Feulgen squash in acetic acid of meiosis in Equisetum maximum Lam. x 1000. 



For further information see Fig. 221. 



There are, however, two difficulties to which attention should be drawn before this 

 number is accepted. In all the large-chromosomed species, that is, in the subgenus 

 Hippochaete, there is a tendency for counts to exceed this number by one or two. For 

 these therefore the number 1 08 is a minimum value. In the small-chromosomed species 

 of the subgenus Eu-eguisetum, on the other hand, the difficulty is the other way. For these 

 the number 108 is a maximum, and one is often tempted to wonder whether the correct 

 value is not perhaps one or two less. The reason for this is perhaps psychological, in that 

 large chromosomes are sometimes more easily misinterpreted than small ones in the 

 direction of excessive subdivision, since very odd-shaped groups can deceptively re- 

 semble two pairs in accidental contact. An example of such a case is marked by an 

 arrow in Fig. 214a, and a very large figure-of-eight pair on the left of the same nucleus 



222 



