INDUCED APOGAMY 



The aim of this chapter will not be to add anything to the morphological aspect of 

 the problems raised by induced apogamy, but merely to amplify the cytological know- 

 ledge relating to two historic examples already mentioned in the above lists, namely, 

 Doodia caudata (Cav.) R.Br, and Scolopendrium vulgare, as used by previous investigators. 



The genus Doodia consists of a group of five closely related species of small tropical 

 ferns, spread from Ceylon to New Zealand and characterized by a soral structure closely 

 akin to Asplenium and Scolopendrium but borne on coriaceous evergreen leaves with the 

 outline depicted in Figs. 203 and 204. Doodia caudata (Cav.) R.Br, itself is native to New 

 Zealand and Australia. It was introduced into European botanic gardens in the middle of 

 last century and had been used for experimental purposes as early as 1887 by Stange. It 

 is not known whether all botanic garden stocks still in cultivation relate back to a 

 common source or whether the species may have been introduced more than once. Un- 

 fortunately, precise records concerning such matters have not as a rule been kept, and 

 therefore the only thing which can be said with certainty about the origin of the material 

 to be quoted below is that it came from Kew in 1938 and is identical with that used by 

 Duncan. 



The morphological part of Duncan's work had involved the induction of apogamy by 

 Lang's method in normal prothalli of D. caudata, which was followed by the induction 

 of apospory on young, detached leaves laid on soil from both apogamously produced 

 and sexually produced plants. None of the new types of sporophyte was kept alive tor 

 long enough to reach fertility and therefore nothing was known about meiosis. Root-tip 

 counts of apogamous plants versus sexually produced plants were, however, successful 

 in demonstrating the gametophytic chromosome number in the apogamously produced 

 plants. This was assumed by Duncan to be the haploid number, but, as will be shown 

 below, this is probably not the case. 



The material for the following observations has been supplied to me by Professor 

 Lang's former research assistant, Mr Ashby, without whom the present chapter would 

 not have been written. After Dr Duncan's departure from the Cryptogamic Laboratory 

 in Manchester, at the end of a year's visit, the old culture pans which had been prepared 

 for his work and which were still in being, were kept under observation by Mr Ashby, 

 and apogamously produced plants were extracted and carefully nursed as fast as they 

 appeared. A very beautiful specimen, detected and photographed by Mr Ashby, is 

 shown in Fig. 202 c, in which one old prothallus may be seen carrying two young 

 sporophytes. The small sporophyte on the right is apogamously produced, while the 

 larger one on the left is sexually produced from a belated fertilization after the apoga- 

 mous plant had already been initiated. Since the larger plant is also the younger, initia- 

 tion of the two in the reverse order being impossible, the difference of size is very clear 

 demonstration of the diminutive stature of the first-formed organs of an apogamous 

 plant. This makes cytological study somewhat difficult, since the roots of such plants are 

 of thread-like thinness. A fortunate specimen, however, gave the plate of chromosomes 

 shown in Fig. 202 e and/, and the very great difference in chromosome number between 

 this and a sexually produced sister can at once be seen by a glance at Fig. 202 b-d. 



With regard to the chromosome numbers themselves, these have not yet been 

 determined with complete finality owing to my own departure from Manchester and 



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