908 



SCIENCE 



[N. S. Vol. XXIX. No. 753 



entation is attained by a series of random move- 

 ments continued until a position favorable to the 

 organism is reached, and not by a direct modifica- 

 tion of the motor mechanism due to the local 

 action of different concentrations of the medium 

 on different portions of the body. This conclusion 

 seems reasonably certain for negative reactions 

 and probably for positive ones. The results ob- 

 tained so far indicate that the movements and 

 reactions of fern spermatozoids are of the same 

 nature as those described for protozoa. 

 Some Aspects of the Mycorliiza Problem: Ben- 

 jamin C. Geuenbeeg, DeWitt Clinton High 



School, New York, N. Y. 



Mycorhiza is found on the roots and under- 

 ground stems in many families of plants. The 

 identity of the fungus in the symbiosis has been 

 determined in but few cases, and in these not 

 always with certainty. 



Many theories as to the relationship between 

 fungus and phanerogam have been offered, but 

 none fits all the facts. It is, however, not to be 

 expected that the mycorhiza has the same signifi- 

 cance in all cases: in the different forms the 

 relationship may be of different types, as nitrifica- 

 tion, humus disintegration, water absorbing or 

 storing, etc. 



To the mycorhizas occurring in plants free from 

 chlorophyll, there has been ascribed the function 

 of obtaining organic nutrients directly from the 

 humus. In several species of Oorallorhiza exam- 

 ined there are present considerable quantities of 

 starch, notwithstanding the entire absence of 

 chlorophyll from the plants. The constituents of 

 the humus that may yield carbohydrates, and the 

 mechanism for the conversion of these materials 

 into starch remain to be determined. 



The solution of certain practical problems, as 

 some in forestry, the transplanting of certain 

 trees, tuberization, nitrification of the soil, etc., 

 may have to wait upon the solution of some of the 

 problems presented by the mycorhiza. 

 The Morphology of Salvinia (preliminary) : 



Wanda M. Pfeiffee, University of Chicago, 



Chicago, 111. 



The early stages in the development of sporo- 

 carps are as described in Juranyi's " Ueber die 

 Entwickelung der Sporangien und Sporen von 

 Salvinia natans" (1873). In the young condi- 

 tion megasporoearps can be distinguished from 

 mierosporocarps only by the relatively smaller 

 number of sporangia which they contain. 



Later stages in the development of sporangia 

 are very different from Juranyi's figures, since the 



tapetum was never observed to become two-layered, 

 although the tapetal cells were often multinu- 

 cleate, and since in no case were there more than 

 eight spore mother cells found in either mega- 

 sporangium or microsporangium. 



The behavior of abortive megaspores was as 

 described by Heinricher, in so far as the position 

 taken by such spores is concerned. The activity 

 of these spores in the formation of the perineum, 

 however, is extremely doubtful since this seems 

 to be entirely built up by the activity of the large, 

 deeply staining tapetal cells. 



The relationship of Asolla and Salvinia is still 

 an open question. 



A Preliminary Account of Dioon spinulosum: 

 Chaeles J. Chamberlain, University of Chi- 

 cago, Chicago, 111.^ 



Dioon spinulosum is a Mexican plant and has 

 been known only from the leaves and some small 

 trunks. The plant was found in abundance at 

 Tierra Blanea and at Tuxtepec in March, 1908. 

 The trunk is often six meters in height and occa- 

 sionally reaches a height of 16 meters. The ovu- 

 late cones are very large, elongated ovoid, about 

 70 centimeters in length and about 30 centimeters 

 in diameter. They often weigh 14 kilos. The 

 sporophylls are comparatively much shorter than 

 in D. edule and the seed much larger. The stam- 

 inate cone is ovoid and measures about 21 X 10 

 centimeters. Material is being secured for an 

 extended study. 



Demonstration of Seedlvngs of Selaginella semper-' 

 mrens: Feancis E. Lloyd, Alabama Polytechnic 

 Institute, Auburn, Ala. 

 A Statistical Criterion for Species and Genera 

 among the Bacteria: C. E. A. Winslow, Massa- 

 chusetts Institute of Technology, Boston, Mass. 

 The existence of an almost infinite number of 

 minute varieties has so far almost nullified any 

 attempt at a natural classification of the bacteria. 

 The vast numbers of generations which succeed 

 each other in a short space of time, the absence 

 of the s\vamping effect of amphimixis and the 

 direct effect of the environment all help to make 

 boundaries indistinct among these simple forms. 

 The attempt has been made by the author and his 

 colleagues to attack the problem by the statistical 

 method, and the genera and species of the Cocea- 

 eeje have been mapped out in the following way: 

 A number of characters (mostly biochemical, for 

 it is precisely along physiological lines that the 

 bacteria have differentiated, as the higher forms 

 ' Investigation prosecuted with the aid of a 

 grant from the Botanical Society of America. 



