Meiosis in Two Different Clones of the Apomictic Chondrilla Juncea

HOSE apomicts whose legitimate embryo-sac mother-cells (EMC'S) T regularly give rise to unreduced parthenogen'etic embryo-sacs could, until quite recently, be divided into two different groups with regard to the first division of the EMC.The first of these groups is represented by a pure mitotic division, which has been studied in Hieracium by the author (1941).The second group is represented by a so-called pseudohomotypic division, which has been studied especially in Taraxacum by GUSTAFSSON (1935, and later), h s to the latter division, two papers have reclently been published by two different workers who have found that GUSTAFSSON'S interpretation of the conditions in Taraxacum must be erroneous, Thus FAGERLIND (1947 c) and BATTAGLIA (1948), at about the same time and independently of each other, have found that the EMC's of Taraxacum divide in a manner very similar to the formation of restitution nuclei in the PMC's of oertain Hieracia, which ROSENBERG (1917, called contraction nuclei.Consequently, one can also call in question other cases where this division has been considlered to occur.Thus FAGERLIND (1947 b) nefers to Erigeron, which has been studied by HOLMGREN (1919), GUSTAFSSON (1935) and the present author (1944) and in which the pseudbhomotypic division has been considered to occur with oertainty.Through his own investigations ( FAGERLIND, 1947 b) and partly on the basis of oertain ,deviating)) division stages published by the author (BERGMAN, 1944) he comes to the conclusion that here, too, we have another case of a contraction nucleus or, as FAGERLIND calls it, a metaphase restitution nucleus.No doubt FAGERLIND is right in his opinion, and one has to agree with him when he calls in question the presence of a pseudohomotypic division, inter a h , in Chondrilla juncea, which until now has also been definitely considered to occur.Until now Chondrilla juncea has been the subject of only a few relatively superficial investigations with regard to the divisions in the EMC's.The last one was made by the author, who for certain reasons Hcrcdlfas X X X V I .20 208 B. BERGMANcould only make a superficial examination at the time (cf.BERGMAN, 1944, p. 249).The division stages discovered aorresponded very well with GUSTAFSSON'S pseudohomotypic division, and therefore it was concluded that probably such a division occurs in Chondrilla, too.On account of the papers of FAGERL~ND and BATTAGLIA, however, the situation is now changed and Chondrilla needs a more profound examination.Such an examination hafs now been carried out by the author and the results are presented in this paper. R08ENBERG (1912)was the first to establish on a cytological basis thce occurrence of apomixis in Chondrilla juncea, but as a matter of fact he says nothing about the first division in the EMC'IS, as he intended publishing a more detailed report later, which hle did nlot finish.A s to the pollen formation, ROSENBERG gives some information which is important for the present work.He says that the PMC's divide only oncc and thlerefore only dyads are formed in the microsporogenesis.,Nur aelten habe ich Tetraden gefund'enx (p.918).In 1933, along with some other Chondrilla species, Ch. juncea was again investigated, but this time by PODDUBNAJA-ARNOLDI.She states (p.71) that the EMC regularly runs through a somatic division but with contracted chromasome; hence the same type of division as HOLMGREN (1919) described in Erigeron cfr.annuus and as GUSTAFSSON (1935, and later) declares to occur in Taraxacum and other apomicts and as he calls pseudohomotypic.With regard to the pollen formation in Chondrilla juncea, PODDUBNAJA-ARNOLDI (p.62) points out that ROSENBERC is wrong in his opinion that only dyads are formed, for in her maierial triads, tetrads and polyads are also present.The material of this investigation comes from two different places, partly from Hortus Bergianus in Stockholm, partly from the botanical garden of Uppsala University.At first it was intended only to study the E M C of Chondrilla, but it was not long befope attention was attracted by the PMC's and their divisions.It was found that in the Stockholm plants the microsporogenusis was nearly always completed with dyads, whereas the Uppsala plants nearly always completed their microsporogenesis with tetrads.Hence, Chondrillri juncea appears in two different clones which differ from each other as to their pollen formation, and evidently ROSENBERG happened to investigate intdividuals of the one clone, whereas PODDUB-NAJA-ARNOLDI investigated individualis of the other.This investigation of the meiosis in the PMC's has shown what was to be expected, namely remarkable differenoes between the two clones, 16015223, 1950, 3,