ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 569 



constantly present. In S. polaris and herbacea the adventitious roots are 

 not attacked by the hyphae, only the slender lateral roots ; the mycorhiza 

 produces a coral-like appearance in the root; the root-tip assumes a 

 hemispherical form ; the root-cap is well developed, but consists of a 

 smaller number of layers than the normal ; the liyphse enter the root 

 immediately behind it, forming a cap composed of a single layer of cells. 

 In Polygonum viviparum the author records the first example of the 

 occurrence of a mycorhiza in a green herbaceous plant. It appears to 

 be constant in this species ; also in Dryas octopetala, where it branches 

 in a coral-like manner. Its occurrence in tbese two species is not con- 

 fined to the Arctic circle. Diapensia lapponica contains an endotropic 

 mycorhizH resembling that of the Ericaceae. In the Arctic Ericaceae a 

 mycorhiza appears to be universal ; the author records it in the follow- 

 ing species : — Azalea procumbent, Andromeda hypnoides, A. tetragona, 

 Ledum palustre, Oxycoccos palustris, 0. 7nicrocarpus, Phyllodoce coendea, 

 Bhododendron lapponicum, Vaccinium uliginosum, V. vitis-idsea. Among 

 Orchideaa it occurs in Habenaria obtusata, H. albida, and Chamseorchis 

 alpina. 



Trichosporum Beigelii.* — P. Vuillemin describes a fungus which is 

 designated Trichosporum Beigelii Rabenhorst. Its pla3tids are thick- 

 walled cells with nuclei varying from 0-8-0-5 /jl, the cells rauging from 

 2-5 ll to 4-5 jx. These cells lie in a mucilaginous matrix derived from 

 the superficial lamella of the membrane. The fungus causes nodosities 

 on hair, and sections made through these nodosities show long series of 

 cells arranged radiately, though on superficial examination they look 

 like a dense irregular reticulum or feltwork. 



Myxomycetes. 



Dictydium umbilicatum.t — E. Jahn has studied in detail the de- 

 velopment of this very polymorphic Myxomycete. The following are 

 the more important points in his observations of the differences be- 

 tween the Cribrarieae (Cribraria and Dictydium), and the remaining 

 Mycetozoa. 



The plasmode contains pigment not found in other forms. This 

 pigment is blue in Dictydium, greenish or nearly black in Cribraria. 

 Dictydium contains granules, found in no other group, of a substance 

 which he calls dictydin, characterised by its remarkable resistance to 

 acids and alkalies. It appears to be a subsidiary product of metastasis 

 which is apparently of further use in Dictydium. They are not of a 

 proteid character, and the author compares them with similar bodies 

 in the Rhizopods. The spores do not germinate. No swarm-spores 

 or myxamoebaa have at present been observed. The cell-wall never 

 gives the reactions of cellulose. The sporanges are not formed by 

 creeping on a stalk, but by the pinching in of an external membrane. 

 It is assisted by bands formed out of the granules of dictydin. 



The Cribrarieae must be characterised, not by the absence of a 

 capillitium, but by the occurrence of the granules of dictydin. Such 

 forms as Tubulina and Licea, although wanting in a capillitium, should 

 not be placed among the Cribrariere. 



* Comptcs Rendus, exxxii. (1901) pp. 1369-71. 



t Ber. Ueutsch. Bot. Ges., xix. (1901) pp. 97-115 (1 pi.). 



