CHAP. II. DIFFERENTIATION OF THALLUS. COMPOUND SPOROPHORES. 55 



the apex of the pileus soon cease to lengthen ; they become the tissue of the middle 

 of the pileus, while as the margin advances the hyphae which run into it send out 

 numerous straight or curved branches upwards and outwards, which in their turn 

 soon cease to elongate and form the general tissue of the pileus (Fig. 24 b). Closely 

 crowded branches from the under surface of the layer which runs into the margin 

 grow at the same time and in the same centrifugal succession from a curved base 

 perpendicular to the under surface of the pileus ; these are the beginnings of the 

 tissue that bears the hymenium and of the hymenium itself. They are at first of 

 uniform length, and the surface of the hymenium is smooth at first, as Hoffmann 

 rightly affirms in opposition to a former incorrect statement of mine, though it only 

 continues so for a short time. The elongation of the hymenial hyphae which 

 grow vertically downwards takes place in alternating radial bands in varying degree. 

 In some it continues longer, and they project beyond the smooth surface as the trama 

 of the lamellae, on which the hymenial elements arise in the position already described, 

 advancing from the base toward the free edge. The hyphal extremities cease to 

 elongate at an earlier period in the intervals between the lamellae, and become 

 directly elements of the hymenium. 



During this growth by terminal and marginal formation of new constituents, the 

 parts at a distance from 

 the growing point or mar- 

 gin enlarge by expansion 

 of their cells, and the tis- 

 sue which is at first uni- 

 form is differentiated at 

 the same time into the 

 several layers of the ma- 

 ture sporophore. It is 

 readily observed that this 

 process of expansion also 

 advances in the stipe from 

 below upwards, and in 

 the pileus from the centre 

 to the margin. To this ex- 

 pansion of the Originally FIG. 24. Jfaricus (CotWa) <tryof*tt,ts. Bu\\. Radial longitudinal section showing 

 ,ro>-ir cm-ill olomenrc rr> the course of the hyphae. a a quite young and entire specimen 1-3 mm. in height ; first 

 ' l beginnings of the pileus. * older specimen with the pileus 2-5 mm. in breadth ; / piece 



several times their former of a lameiu. siightiy magnified. 

 size is due in great part, 



especially in rapidly growing fleshy sporophores, that enlargement which may be seen 

 with the naked eye. In Agaricus (Mycena) vulgaris for instance I succeeded in deter- 

 mining, by measurement of the cells and counting their number on the transverse 

 section, that the increase in length and breadth of the stipe, which becomes on an 

 average 50-60 mm. long, from the time when its length was about 3 mm. and its 

 cells could be exactly measured, must be almost exclusively due to extension of 

 the cells. I obtained the same result in the case of Nyctalis parasitica ; the conclusion 

 was similar in the case of Agaricus (Collybia) dryophilus, Bull., but less precise 

 on account of the very unequal length of cells placed at the same height. Exact 

 measurements can scarcely be made in the pileus owing to the curvatures and 

 want of uniformity in the cells, but here too it is evident that there is an expansion 

 of the tissue-elements, which often exerts considerable force and advances towards 

 the margin. It appears to me to be doubtful whether there is also any formation 

 of new cells by transverse division of the primary cells of the hyphae and by pro- 

 duction of new branches in parts removed from the margin. It does not take place in 

 either of the two cases just mentioned, but they are too isolated to allow of our 

 drawing a general conclusion from them. Branches often occur on hyphae which 



