One other form of brand (_Xenodochus carbonarius_), presenting, it is believed by some, generic differences from all that we have as yet noticed, remains to be briefly alluded to. This form appears to be very uncommon in this country, but, when found, is parasitic on the leaves of the great burnet (_Sanguisorba officinalis_), a plant of local distribution. The parasite appears to the naked eye in small tufts or pustules resembling those of an _Aregma_, but, when microscopically examined, the cells of the spores are found to be numerous, indeed, considerably more than in the most complex _Aregma_ (fig. 29). This, however, seems to be the only distinction, for the cells are free in the interior of the investing membrane, and in all points of structure, in so far as it has been examined, identical with _Aregma_. Whether it is logical to consider a four-celled spore an _Aregma_, and a seven-celled spore an _Aregma_, and exclude a ten or twelve-celled spore from the same genus on account of the number of its cells, does not appear to us clearly answerable in the affirmative. During the course of this and the preceding chapter we have passed rapidly through four genera of parasitic fungi so nearly allied, that one is almost led to doubt the validity of the generic distinctions. These may be presented briefly thus:— Spores two-celled PUCCINIA. Spores three-celled TRIPHRAGMIUM. Spores four to AREGMA. seven-celled Spores many-celled XENODOCHUS. It has been seen that the habit, mode of growth, germination, and structure, except in the number of cells, scarcely differ; but it is not our province here to enter upon the discussion of such a subject. The association of one-celled, orange-coloured spores with the brown two or more celled spores passed in review is another feature worthy of a passing notice, and which opens a field for discussion. It is generally admitted that these two forms are the production of the self-same mycelium or vegetative system, but it is not so generally admitted that they are but two forms or phases of the fruit of the same plant. It is not at all uncommon in the history of mycology to find two forms which were for a long time considered to be distinct plants producing different forms of fruit, and which bore different names, and were located in different genera, at length proved to be only the self-same plant in different conditions, and ending in one name being expunged from the list. Such a fate probably awaits, at no distant date, the orange spores which precede or accompany the species in the present genera. Already Tulasne and some others accord them no place in their system.