February 20, 1914] 



SCIENCE 



291 



ter plant is unknown, but it was probably brought 

 from Borneo. 



Macroglossum differs from Angiopteris in sev- 

 eral important respects. It has simply pinnate 

 leaves, much more like Dancea than Angiopteris. 

 The sporangia, while distinct, are quite different 

 from those of Angiopteris, and closely resemble 

 those of Archangiopteris The number of sporangia 

 dn the sorus is much greater than in Angiopteris, 

 •sometimes exceeding 60. The indusium is also 

 much better developed than in Angiopteris. There 

 are also some important anatomical differences in 

 the leaf structure. 



Macroglossum is a large fern, the leaves being 

 about four meters in length. In habit it resembles 

 a gigantic Danma — and also suggests strongly 

 some of the larger species of Zamia. The leaflets 

 reach a length of over 50 centimeters. 



The prothallia are very large, sometimes nearly 

 three centimeters in length by two in breadth. 

 They are moncecious. The antheridia are very 

 large, but otherwise much resemble those of Angi- 

 opteris, as do the archegonia. The embryo has a 

 ■conspicuous suspensor. 



Macroglossum undoubtedly belongs to the Angi- 

 opterideas, but its affinities are rather with 

 Archangiopteris than with Angiopteris. Like 

 Archangiopteris it suggests a distant relationship 

 to Danwa. 



Morphology of Thismia (Bagnisia) americana 



n. sp.: Norma E. Pfeiffer. 



Among the BurmanniaeeEe the forms closely re- 

 lated to Thismia americana have been found up to 

 date only in the southern hemisphere, mostly in 

 the Malay Archipelago. The particular subdi- 

 vision to which this Thismia shows affinities has 

 "been for the most part discovered in recent years. 

 The finding of one in a region so remote from the 

 home of its relatives as Chicago, augurs well for 

 the possibility of other undiscovered forms. The 

 reduced size and anatomy of this saprophytic form 

 are noteworthy. The floral axis arises simultane- 

 ously with a, secondary root from the main root. 

 The structure of the flower is similar to that of 

 other Thismias of the Bagnisia section. Floral de- 

 velopment is somewhat similar to that in the 

 Orehidaeeae, to which resemblance in other fea- 

 tures is evident. The characters are deemed suffi- 

 ciently distinctive to warrant the establishment of 

 a new species. 



Some Observations on the Anatomy and Other 

 Features of the Black Knot: Alban Stewart. 

 Enlargements, popularly known as "black 



knots, ' ' are formed on the branches of Prunus vir- 

 giniana L. and other species of cherries, by the 

 attack of the fungus Plowrightia moriosa (Sehw.) 

 Sacc. These knots may arise primarily through 

 the infection of the branch by means of spores, or, 

 secondarily, by the spreading of the fungus 

 through the tissues from a knot already formed. 



Normal wood of P. virginiana usually contains 

 rays from one to four cells wide in cross section. 

 As a result of the stimulating action of the fungus 

 these rays may become much broader in infected 

 tissue, simulating the structure of compound rays. 

 The production of the usual elements of the xylem 

 is greatly inhibited during the first season 's growth 

 of the knot, but there is a correspondingly great 

 production of xylem parenchyma, which is almost 

 absent from normal wood. By further increase in 

 size of parenchyma cells the knot is greatly en- 

 larged during the second season of its develop- 

 ment. The cambium is pushed outward by this 

 means, and with it are isolated groups of fibers 

 and other xylem cells. There is also an abnormal 

 growth of the ray tissue at about this time, which 

 ruptures the cambium, opposite the rays, and 

 pushes segments of it outward into the bark. By 

 further division of these misplaced cambium cells, 

 various xylem elements are produced in the bark 

 very much out of their normal position. The seg- 

 ments of the cambium, which remain between the 

 rays, retain their relative position throughout the 

 subsequent development of the knot, and give rise 

 to wedges of xylem each of which is subtended by 

 a mass of phloem on the outside. 



There is apparently no abnormal growth in the 

 outer portion of the bark. It is sloughed off just 

 before the conidia are produced. 

 Homologies of the Froiid in Lemna: Frederick 



H. Blodgett. 



The plant body in Lemna has been considered 

 by various authors as a leaf, a stem or a combi- 

 nation of these, but in most cases little morpho- 

 logical evidence is advanced for one or the other 

 idea. The structure of the frond, especially during 

 its early stages, is used as the basis of a discus- 

 sion of the parts present. It is concluded that the 

 frond represents a single leaf at the tip of a stem 

 of one internode, at the tip of which a dichasial 

 stem apex is located, and ventrally an adventitious 

 root developed. The dichasial buds are protected 

 by the sheath or pouch of the frond, which de- 

 velops simultaneously with the buds, from the 

 tissue immediately about the insertion of the buds 

 upon the apical tissues, becoming congenitally 



