386 



SCIENCE 



[N. S. Vol. XXXVII. No. 949 



on one side of the cell. The degree to which 

 these spines are developed in a given colony is 

 determined by cellular interactions. The degree 

 to which the tendency is present in different 

 species is the basis for the delimitation of species 

 in the genus. All the cells show also a polar 

 differentiation, the spines being produced in the 

 direction of the shorter of the two major axes of 

 the cell. There is some evidence also of spe- 

 cifically oriented attractions between the cells 

 such that the spines in normal individuals come to 

 point radially outward in the interior as well as 

 in the peripheral cells of the colony. Specifically 

 inherited cell form and cellular interactions during 

 growth are the principal morphogenetic factors in 

 the development of the differentiated cell colonies 

 of Pediastrum. 



Tetradesmus, a New Four-celled Ccenohio Alga: 



G. M. Smith, University of Wisconsin. 



Tetradesmus resembles Scenedesmus in the num- 

 ber and shape of the cells, but differs from it in 

 the cellular arrangement, the cells being in two 

 planes, each plane containing two cells. 



The reproduction is by antocolonies. The first 

 cleavage of the mother cell is transverse and the 

 second is in the same plane and diagonal to the 

 line of the first cleavage. After the four daughter 

 cells have been formed by cleavage they elongate, 

 while still within the mother cell, taking the same 

 relative position that they have in the mature 

 colony. The young colony is liberated by a longi- 

 tudinal rupture of the mother cell wall. 



The mature cell possesses a nucleus and a pyre- 

 noid. The nucleus divides once before the first 

 cleavage takes place, but the pyrenoid does not. 

 When the four daughter cells have been formed, 

 the old pyrenoid of the mother cell is found in one 

 of them while the other three contain no pyrenoid. 

 This pyrenoid then disappears and pyrenoids are 

 formed de novo at the time that the daughter cells 

 are elongating prior to their liberation from the 

 old mother cell wall. 

 The Belation of the Lichen to its Algal Host: 



Beuce Fink, Miami University. 



The common algal hosts of lichens; finding the 

 algal hosts growing near lichens in nature; cul- 

 tures of lichens from spores and spermatia with 

 and without the algal hosts; cultures of the algal 

 hosts separately; growth of lichen hosts and other 

 alg£e on media with and without light and carbon 

 dioxide ; breathing pores and other means of aera- 

 tion of the algal hosts in lichens; lichens as car- 

 riers of food to the algal hosts; hypotheses regard- 



ing the relationship of the lichen and its algal 



host, with evidence from recent research. 



A Dry Bat of the Irish Potato Tuier: E. M. 



Wilcox, University of Nebraska. 



In 1908 our attention was called to the fact 

 that potatoes grown in western Nebraska were 

 often seriously injured by a form of rot during 

 storage. Comprehensive investigations were under- 

 taken to learn the exact cause and nature of this 

 disease. It was found to be due to a new species 

 of Fusarium, shortly to be published as Fusarium 

 tuberivorum Wilcox and Link. Numerous inocula- 

 tion experiments have established the causal rela- 

 tion of this organism to this tuber dry rot. The 

 organism is, however, unable to invade any other 

 part of the plant than the tuber, and the tuber 

 only when it is practically mature. 

 The Propagation of Medicinal Plants: F. A. 



Miller. 

 An Optimum Culture Medium for a Soil Fungus: 



J. B. Pollock, University of Michigan. 



The work was done in collaboration with Miss 

 Rose M. Taylor, and had for its object the deter- 

 mination of an optimum culture medium of ex- 

 actly known composition and of simple constitu- 

 tion. The fungus chosen was one isolated from the 

 soil by H. N. Goddard, and determined as a new 

 species of Myceliophthora, to be described by him 

 elsewhere under the name of Myceliophthora sul- 

 phurea. The medium aimed at was one with the 

 fewest and simplest compounds which would fur- 

 nish the chemical elements necessary for the 

 growth of fungi. It is known that fungi will 

 grow with as few as eight of the known elements, 

 namely, carbon, hydrogen, oxygen, nitrogen, sul- 

 phur, phosphorus, potassium and magnesium. In 

 the experiments sixteen organic compounds were 

 tested as to their availability for carbon, and inci- 

 dentally they could also supply hydrogen and 

 oxygen. These carbon compounds were saccharose, 

 dextrose, maltose, inulin, Isevulose, arabinose, man- 

 nite, cellulose, resin, starch, glycocoll, alanin, 

 asparagin, glycerine, potassium tartrate and so- 

 dium benzoate. The compounds tested as to their 

 availability for nitrogen were ammonium sulphate, 

 ammonium nitrate, sodium nitrate, potassium ni- 

 trate and calcium nitrate. In all the cultures 

 magnesium sulphate was used to supply mag- 

 nesium and sulphur. This was used in only one 

 concentration, 1/1000 that of a gram-molecular 

 solution = 1/1000 M. Mono-potassium phosphate 

 was used to furnish phosphorus and potassium, 

 and it was used in several concentrations, 1/10, 



