The Microscope. 25 



In its sporangia the extra-matricular portion has more or less 

 the shape of a long-stalked pear, and is not unicellular but is di- 

 vided into two by a partition, the lower, slender part representing 

 the stem, the upper ventricose one the sporange. In the latter are 

 developed from fifty to eighty small swarm spores, and as these 

 mature the vertex of the sporange becomes chemically altered, 

 at their maturity the membrane being dissolved ; the spherical 

 swarm spores then escape, each being provided with a large nu- 

 cleus and a posterior cilium. 



The intra-matricular part consists of a delicate mycelium, 

 which is obscured by the altered contents of the Pinmdaria 

 frustule, yet in completely exhausted host-plants it can be seen 

 in |its coarser ramifications, without the aid of reagents. Its 

 effect on the host is of the usual character, the most striking 

 changes occurring in the chromatophores, which become broken 

 up and transformed into dirty red-brown or olive-colored clots, 

 and in part altogether disappear. 



The extra-matricular portion which consists of the pedicle-like 

 cell and the spherical sporange, is formed from the swarm spore 

 in the following manner: The pole directed away from the host 

 developes into a cylindrical sac constricted above its base. The 

 free end bulges out, the contents withdraw toward the bulged por- 

 tion, and the transverse partition arises and separates the now 

 empty stalk from the sporangial sac. It is this exceedingly pe- 

 culiar development from the zoospore that has induced the au- 

 thor to place the fungus in a new genus. No resting condition 

 of the plant has been seen, either by collection in the autumn 

 or by cultivation. 



The spots chosen for penetration into the Diatom are always 

 either the non-silicified border between the girdle-band and 

 valve, between the two girdle-bands themselves, or through the 

 middle line (raphe) of the valve. The raphe is said to be a 

 longitudinal cleft, otherwise the fungus could not penetrate the 

 Diatom at that point, as it does, usually selecting that portion of 

 the cleft near the centre of the Pinnularia, from six to ten indi- 

 viduals often being attached to each side of the frustule near 

 that point. When the fungus invades very small Navicular 

 forms, both mycelium and fructification are dwarfed. It also oc- 

 casionally happens that the extra-matricular portion is not 



