10 



BRITISH MYCET0Z0A. 



plate and the interior of the glass shade. It it is in sufficient 

 quantity, it will in the course of a couple of days cover the glass 

 with a network of veins over an area of perhaps forty or fifty square 

 inches. A piece of fresh Steream, soaked in water, may now be 

 inserted beneath the shade, allowing it to come in contact with one 

 of the smallest veins. In a few hours the whole of the plasmodium 

 will have withdrawn from the sides of the shade, and concentrated 

 itself on the fresh food in a dense yellow mass. The length of time 

 during which the plasmodium will continue to feed and increase 

 in bulk before changing into sporangia differs according to the 

 species, and also to the conditions of its surroundings. Physarum 

 psittatinum, which inhabits the rotten stumps of old trees, appears 

 to pass twelve months in the plasmodium stage ; on the other hand, 

 Didymium diffor»ie will go through the several stages from germina- 

 tion of the spores to the formation of the sporangia in a fortnight. 

 The latter species is very common, and may easily be cultivated. 

 The spores can be sown in water on a thin cover-slip supported 

 over a glass slide by a ring of wet blotting-paper, the required nutri- 

 ment being supplied by two or three slices of the mucilaginous coat 

 of a garden-cress seed. In this moist chamber the whole process of 

 the division of the swarm-cells, their coalescence to form the plas- 

 modium, and the construction of the sporangia, may be watched 

 under the microscope. 



The plasmodium, if allowed to dry, passes into the sclerotium 

 or resting stage. The sclerotium of Badhamia atricularis is dull 

 orange-red in colour, of horny consistence, made up of a multitude 

 of thin-walled cysts closely packed together ; each cyst is filled with 

 granular protoplasm, among which ten to twenty nuclei are inter- 

 spersed. On being wetted the sclerotium will revive in the course 

 of a few hours and resume the streaming movement. Preserved in 

 a dry state, it will retain its vitality for three or four years, but it is 

 longer in reviving according to the length of time it has remained in 

 the resting condition. 



The formation of the sporangium may be illustrated by the 

 growth of Comatriclia obtusata, a common species which is often 

 found on the under side of fir planks that have been left to rot on 

 the ground. When the fruiting period arrives, the watery-white 

 plasmodium issues from the wood at a point favourable to the 

 development of the sporangia, and spreads over an area measuring 

 perhaps half an inch across. After a time the plasmodium is seen 

 to concentrate in thirty or forty centres, and in an hour or two each 

 centre has risen into a pear-shaped body with a narrow base, a dark 

 stalk being just apparent through the translucent white substance. 

 In six hours the black hair-like stalk has grown to its full length, 

 bearing at its summit the young sporangium, consisting of a white 

 globule of viscid plasma with a diameter about one-fifth of the length 

 of the stalk. A pink flush now begins to pervade the sporangium, 

 caused by the formation of the dark flexuose branching threads ot 



