THREE SPECIAL CASES OF FERN HYBRIDS: 



Investigation of the purest forms of the parent species in the alpine garden showed 

 that the cytological nature of these was exactly as in England (cf. p. 92), P. Lonchitis 

 being a diploid species and P. aculeatum tetraploid. This may perhaps be sufficiently 

 demonstrated by Fig. 157a and b, which are from the original fixings made on the 

 journey in 1937. These fixings are very inferior in quality to those otherwise obtain- 

 able, but as an addition to what has previously been given in Chapter 6, they will 

 perhaps serve as a rough demonstration that the two species on the Continent, as in 

 Britain, dififer in chromosome number. This circumstance is a very fortunate one, 

 since a simple root-tip count should confirm or refute the correctness of the diagnosis 



Fig. 156. Series of pinnae from dried wild fronds of different adult plants from one locality (Les 

 Plans sur Bex, Switzerland) to show range of form of hybrid Polystichum. a. P. Lonchitis (L.) Roth. 

 b, c. P. illyricum Hahne. d. P. aculeatum (L.) Roth, ( = P. lobatum (Huds.) Woynar). 



of the putative hybrid, for P. illyricum, if it really is the interspecific cross between 

 P. Lonchitis and P. aculeatum, ought to be a triploid with 123 chromosomes in its roots. 



Among the plants suspected to be P. illyricum on morphological grounds three were 

 shown to be triploid by root-tip counts. It had, however, been at once apparent from 

 scrutiny of the living populations before collection that a considerable range of morpho- 

 logical types grading between the pure forms of the putative parents could be found, 

 and since a number of these had also been sent to England it was not surprising to find 

 that not all were actually triploid. In the 1937 visit one suspected hybrid, rather closer 

 than the average to P. aculeatum, turned out to be a tetraploid, while on the 1947 visit 

 two plants rather closer to P. Lonchitis than usual, though with more deeply cut-up 

 pinnae, proved on examination to be diploid or nearly so. Some examples of the range 

 of pinnae found on the 1947 visit are shown in silhouette in Fig. 156, in each case the 

 pinnae chosen being from large fertile fronds. The parental types, together with diploid 

 and triploid putative hybrids, are represented, and they obviously make an almost 

 continuous morphological series. 



152 



