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BOTANICAL GAZETTE

AUGUST, 1905

SPOROGENESIS IN PALLAVICINIA.

CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY.

LXXV.

ANDREW C. MOORE.

(WITH PLATES III AND IV)

THE presence of a quadripolar spindle in the division of the spore mother cell of Pallavicinia decipiens was announced by FARMER in 1893, and in 1894 he published his detailed studies upon the same plant. The most remarkable feature of these papers is the significance which the author attributes to a quadripolar spindle as a means for the simultaneous distribution of the chromatin to the four daughter cells which become the spores.

According to FARMER'S account (5, 6), the structure in question is developed quite early, before any evidence of approaching division is visible in the nucleus. Later the nucleus becomes lobed, and finally four chromosomes make their appearance. The number is increased by division to eight, which point off in pairs to the four lobes of the spore mother cell. "A further doubling of the chromosomes occurs, so that four of these bodies. . . . go to form the nucleus in each spore. The whole process is very much crowded up, the four-rayed spindle persisting to the end; and even after the exodus of the chromosomes, traces of it can still be seen converging to the original center.'

The presence of a quadripolar spindle is of itself not surprising, since tripolar, quadripolar, and multipolar spindles have been frequently described by various authors; but in every case these structures represent early stages in the development of the achromatic figure and later become normal bipolar spindles. The peculiar

interest attaching to the structure described by FARMER is the reported distribution of the chromatin simultaneously to the four daughter nuclei. If his observations and his interpretation of the spindle are correct, Pallavicinia occupies a unique position among plants and animals.

FARMER (7) sought through a study of other liverworts to throw further light on this subject. He found the quadripolar spindle present in Aneura pinguis, A. multifida, Scapania undulata, Fossombronia, and in other types of the Jungermanniales, but in no case did he find it persisting and functioning, as in Pallavicinia, in the simultaneous distribution of the chromatin. In these forms, according to his interpretation, the ends of the quadripolar spindle fuse in pairs and the distribution of chromatin takes place in the usual manner through two successive mitoses. While not directly confirming his results on Pallavicinia, FARMER thinks the conditions found in these plants strengthen his position. He regards them as representing transitional stages between the normal type of division and the very unusual type which he reports in Pallavicinia. CAMPBELL (I) and other authors generally have accepted FARMER'S

account.

DAVIS (4) from an investigation of Pellia was led to question FARMER'S Conclusions. He regards the quadripolar spindle as a condition of prophase, and believes that it is always followed by two successive mitoses after the usual manner in the spore mother cell, each with a normal bipolar spindle. FARMER (8) is not willing to exclude the four-rayed figure from the spindle apparatus or to employ the term spindle in the restricted sense of DAVIS; but the main features of the discussion are not the questions as to when the achromatic structure becomes a spindle and as to the limitation of this term as a matter of usage-points upon which authors may readily disagree. The fundamental differences between the views of DAVIS and FARMER lie in the history of the quadripolar spindle, and the method by which the chromatin in the spore mother cell is distributed to the four spores. FARMER positively asserts that the quadripolar spindle retains its form and that the chromatin is distributed simultaneously to the four daughter nuclei. DAVIS believes that the quadripolar spindle is a condition of prophase which is followed by two successive

mitoses, each with bipolar spindles, by which the chromatin is distributed in the usual way within the spore mother cell. Apart from the rapidity of the two mitoses and the prominence of a fourrayed achromatic figure in the prophase of the first, the latter author holds that there is no essential difference between the processes of sporogenesis in Pallavicinia and in other liverworts and higher plants. DAVIS (4a) further maintains these opinions in his recent review of the events of nuclear division within the spore mother cell.

In view of the unusual character of FARMER'S results and of the fact that doubt has been expressed as to the accuracy of his observations and their interpretation, I have undertaken an investigation of Pallavicinia Lyellii, believing that evidence obtained from the study of another species of the same genus would help in clearing up the disputed points. Some of my results (15) have already been published, and they do not confirm FARMER in his main contention, namely, the simultaneous distribution of the chromatin.

Pallavicinia Lyellii is a cosmopolitan species which I have found growing abundantly near Columbia, S. C., and in the vicinity of Woods Holl, Mass. The young sporophytes make their appearance in the early fall and mature about the first of April. The material was fixed in chromo-acetic acid and stained with saffranin and gentian violet alone, or in the triple combination of saffranin, gentian violet, and orange G. Iron-alum haematoxylin was also used after the method of Haidenhain. Upon the whole the last-named stain has given the best results. The fibrillar structures are not so well brought out by it as by the gentian violet, but the chromosomes are much more clearly differentiated.

The spherical resting nucleus occupies a central position in the distinctly four lobed spore mother cell. It enlarges considerably preparatory to division and becomes somewhat angular, extending into the lobes of the spore mother cell. At the period of synapsis the nucleolus is conspicuous for its size and prominence (fig. 1), as is also the confused tangle of chromatic threads. The spore mother cell is not so deeply lobed as FARMER (8) figures for Pallavicinia decipiens, and Davis (4) and CHAMBERLAIN (2) for Pellia.

FARMER did not observe the spirem of Pallavicinia decipiens. In P. Lyellii it is exceedingly well-developed, and immediately after