8 A Monograph of the Myxogastres. 



presented during the growth of the primary mycelium is the 

 gradual tapering of the hyphae ; this tapering is of a two-fold 

 nature; the main trunk, or first portion emitted by the spore 

 produces secondary thinner branches, these in turn bear still 

 thinner branches, and this production of successively thinner 

 hyphae results in a complex structure, which may be compared 

 to the branching of a tree, commencing with the trunk and 

 ending with the youngest and thinnest ramifications. The 

 second type of tapering is seen in the gradual attenuation of the 

 component hyphae ; this is most conspicuous in the case of 

 elongated, unbranched hyphae, which from a basal width of 

 8 — 10 \i taper gradually towards the apex, which may not exceed 

 2 /lA in width. If a spore of Mucor lateritius, a species met with 

 on semi-putrid potatoes, be sown on a glass slip in a drop of 

 sterilized decoction of decayed potato, and kept in a damp 

 atmosphere under a small bell-jar, growth proceeds somewhat as 

 described above ; a dense mycelium showing the two aspects of 

 attenuation is developed; and as growth proceeds an irregular 

 reticulation is formed, due to the coalescence of originally 

 distinct lateral branches. This coalescence is not confined to 

 cases where two hyphae happen to meet in the ordinary course 

 of growth, but in many instances, as described in detail by 

 Professor Marshall Ward in the instance of a species of 

 Botrytis} the hyphae attract each other, and may be deflected 

 from their previous course through a right angle or even more. 

 The peripheral hyphae usually elongate for some distance in 

 straight lines, the unknown factor in connection with coalescence 

 being apparently absent from the youngest portions, and only 

 manifests itself at some distance behind the tips of the hyphae, 

 where it possibly determines first the origin of lateral branches, 

 and subsequently their direction. This yearning for coalescence 

 is not common to all lateral branches. The hyphae possess a 

 cell-wall but no transverse septa, hence the protoplasm is 

 continuous throughout the intricate mycelium, and, as would be 

 expected, the cell-wall is exceedingly thin and yielding, and 

 becomes very pale blue with iodine, and very pale brownish- 



1 A Uly-ditiease. Annals of Botany, vol. ii. pp. 319—378, 5 plates. 



