Febbuaet 3, 1911] 



SCIENCE 



193 



fairly well known, comparatively little attention 

 has been given to the structure of the adult plant, 

 doubtless on account of the difficulty of securing 

 material. 



In an adult stem of Zamia floridana 5.5 cm. in 

 diameter the zone of vascular tissue was 2.5 mm. 

 in width. In a plant of Geratosamia inexicana 

 with a stem 14 cm. in diameter the zone meas- 

 ured 5 mm. in width. In Dioon edule a stem 

 21 cm. in diameter showed a vascular zone 9 mm. 

 wide. Compared with these narrow zones, the 

 vascular zone in Dioon spinulosum is surprisingly 

 wide, reaching a width of 7.5 cm. in a trunk 

 32 cm. in diameter. 



In Dioon spinulosum there are definite growth 

 rings but they are not annual, for not more than 

 one ring is formed in a dozen years, or perhaps in 

 twenty. Medullary rays are as prominent as in 

 a dicotyl. Dioon edule also shows growth rings 

 but they are not so prominent as in D. spinu- 

 losum. No growth rings were found in the speci- 

 men of Ceratozamia. 



In none of these specimens were there any zones 

 of wood in the cortex. It is possible that tie 

 periodicity which in Cycas produces a zone of 

 wood in the cortex, produces in Dioon a growth 

 ring resembling the annual ring. 

 Spruce Burls: Hermann von Schbenk, Missouri 

 Botanical Garden. 



The author describes some burls observed in 

 certain parts of Maine and Minnesota on the 

 white spruce. They occur on all parts of an 

 affected tree, either singly or in large numbers on 

 one tree. The external appearance of the burl is 

 described and their internal structure. Attention 

 is called to the formation of diamond-shaped 

 holes, which are probably the result of unequal 

 " strains. 



The Origin of the BlepharopJast in Polytrichum: 

 C. E. Allen, University of Wisconsin. 

 A dark-staining granule, the center of a system 

 of radiations, appears in the cytoplasm of each 

 cell of the penultimate antheridial generation. In 

 previous cell generations there were kinoplasmic 

 bodies of varying forms whose behavior was defi- 

 nitely related to spindle formation; but no struc- 

 ture that seems genetically related to the centro- 

 some-like body that participates in the final 

 division. 



This central body divides; the two daughter 

 granules, each surrounded by an aster, diverge 

 until they lie at opposite sides of the nucleus, and 

 a rudimentary spindle appears between them. 

 The central bodies are conspicuous until about the 



time of the disappearance of the nuclear mem- 

 brane; from this time on, they stain less deeply; 

 some of the polar radiations disappear; and, 

 although a granule can usually be recognized at 

 either spindle pole which is probably the central 

 body already described, its identity is often un- 

 certain; and sometimes no such granule is visible. 

 After cell division is completed, a conspicuous 

 body is again visible in each daughter cell, usu- 

 ally appearing to lie in the neighborhood of the 

 former spindle pole; this body functions as a 

 blepharoplast. There seems no reasonable doubt 

 that the blepharoplast is identical with the pre- 

 viously present central body, which persisted dur- 

 ing the division of the mother cell, although the 

 lessened affinity of the central body for stains 

 made it less conspicuous at certain stages. 

 The Method of Chromosome Reduction: R. R. 

 Gates, Missouri Botanical Garden. 

 I have previously suggested that in some plants 

 reduction takes place by telosynapsis, and in 

 others probably by parasynapsis. Comparative 

 studies have confirmed this view, but the difi'er- 

 ence between telosynapsis and parasynapsis is not 

 believed to be of hereditary or phylogenetic sig- 

 nificance. Rather is it merely a matter of cell 

 mechanics, long, threaa-like chromosomes usually 

 pairing side by side and short ones end to end. 

 The only essential and universal feature of meiosis 

 is the segregation of the members of homologous 

 pairs of whole somatic chromosomes. The func- 

 tion of synapsis is not to bring about a pairing of 

 these homologous chromosomes, because they are 

 paired throughout the sporophyte or soma. 

 Neither is it to efi'ect an interchange of chromo- 

 meres or other particles, since the chromosome is 

 considered the unit of morphological nuclear 

 structure ; or even of " influences," since this 

 could take place equally well or better in any 

 " resting " nucleus. Synapsis is, therefore, not 

 the final delayed act of fertilization, and is not 

 of fundamental significance in tne life cycle- It 

 is, partly at least, explained by the clianffe in the 

 karyoplasmie relation which takes place during 

 synapsis, owing to the fact that a segregation of 

 chromosomes is intercalated between two ordinary 

 mitoses. 



On the Organization and Reconstruction of the 

 Nuclei in the Root-tips of Podophyllum pel- 

 tatum: James Beetkam Overton, University of 

 Wisconsin. 



Although a number of valuable papers, dealing 

 with vegetative nuclear divisions, have recently 

 appeared, notably those of Van Wisselingh 



