310 ATKINSON— MORPHOLOGY AND [April 23, 



ment; (3) the differentiation of parts in the primordial ground 

 tissue ; and (4) the origin and development of the lamellse. The 

 peculiar form and position of the annulus on the stem has sug- 

 gested a resemblance to a volva, a structure not admitted in the genus 

 Agaricus as now limited; while the subject of the origin and de- 

 velopment of the lamellze has acquired new interest in all of the 

 Agaricaceas since the accuracy of observations and the correctness of 

 the statements covering a period of more than a half a century, in 

 regard to this topic, have recently been called in question. Without 

 further preliminary remarks we may proceed to an account of the 

 present investigation, and to a consideration of the various matters 

 involved. 



I. The Duplex Annulus and its Significance. 



The Annulus. — The annulus is situated near the middle of the 

 short stem, or even near its base. It is usually very thick next the 

 stem and is divided into an upper and lower limb by a deep marginal 

 groove as is clearly seen in the photographs reproduced in Plate I. 

 In those cases where the annulus is near the base of the stem. Peck 

 was impressed by its suggestion of "the idea of a volva" (/. c, 45). 

 Before the expansion of the pileus, while the veil is still attached to 

 the stem and pileus margin, a longitudinal section of the plant shows 

 very clearly that the lower Hmb of the annulus Hes on the outer 

 (upper) side of the pileus margin (see Plate VII., upper right hand 

 and lower left hand figures). The marginal veil is very thick and 

 the epinastic growth of the pileus margin crowds the latter into the 

 veil tissue and against the stem. The position of the lower Hmb of 

 the annulus therefore corresponds to that of the volva limb of the 

 Amanitas. 



The plates represented in the upper group of Plate VII., were col- 

 lected on the Cornell University campus, those in the upper group 

 during August, 191 1, along a path in the edge of a small wood not 

 far from the street; those in the lower group, July, 1913, along the 

 street railway and parking by East Avenue. In the expanded speci- 

 mens, the pileus ranged from 6 cm. to 8 cm. in diameter. The 

 plants were smaller than those represented in Plate VIII., but since 

 they were abundant and in all stages of development they present in 



