484 THE AMERICAN NATURALIST. [Vol. XXXIX. 



botanists of the Carney Institute, Gr^goire and Berghs. To 

 the writer the conclusions of the second school seem better 

 founded and we shall present them first. Allen's last paper 

 (:05) gives the most complete statement of their interpreta- 

 tions. 



Allen's conclusions (: 03, :os) are based on the study of the 

 pollen mother-cell of Lilium canadense and his account of 

 synapsis in this form is of great interest for the simplicity of 

 his explanation of the events of this phenomenon and their sig- 

 nificance. The nucleus of the young pollen mother-cell follow- 

 ing the last mitosis in the archesporium and previous to synapsis 

 contains a network of large irregular masses connected by fibers 

 of varying thickness. The irregular masses, which probably 

 contain both chromatin and linin, are derived from the chromo- 

 somes of the previous mitosis but these structures cannot be 

 recognized in the resting nucleus. Nucleoli are present among 

 the irregular masses or chromatin knots but are readily dis- 

 tinguished from them. As the nucleus grows larger the chroma- 

 tin knots become more widely separated, but synapsis does not 

 occur until it has reached its full size. 



During synapsis the reticulum becomes transformed into a 

 definite spirem. The fibers connecting the chromatin knots 

 increase in length and become more uniform in thickness while 

 the knots become less conspicuous as though their material were 

 drawn out along the fibers. The fibers of the reticulum are now 

 seen to arrange themselves in pairs and a general contraction 

 of the network takes place which is the beginning of synapsis. 

 Allen believes that this contraction is associated with the approx- 

 imation of the fibers. The contracting network occupies at first 

 the center of the nucleus but later moves to the periphery where 

 the nucleoli may be found flattened against the membrane. 

 There is now a continuous spirem in the nucleus, plainly com- 

 posed of two slender threads lying side by side and probably 

 with no free ends. These two threads often run closely parallel, 

 sometimes loosely twisted about one another, sometimes in con- 

 tact and apparently fused and sometimes rather widely separated. 

 It is clear that the double nature of the thread is not due to a 

 fission but that two independent threads are developed indepen- 



