The North American Slime-Moulds Part 70

e. It has been shown[40] that the process of cell-division in the spore-plasm of the myxomycete is not dissimilar to that obtaining under the same conditions in higher plants. On this supposition we have explanation of spore-division in _Ceratiomyxa_ and can understand the adherence of spores now and again notable. Once the latter phenomenon was thought peculiar to the genus _Badhamia_; but the unsculptured epispore of the spores of reticularias, tubiferas, etc., suggest the same thing and more recently we find it in _Dianema_ and in the _Stemoniteae_; even _Stemonitis_ arrives with cl.u.s.tered spores in groups of four, and we are in sight of a generalization wide.

It is interesting to note that something of this sort was observed by at least one student long ago. Schumacher, _Enum. Pl. Sell._ 2, p. 215, describes _Arcyria atra_ with the characters of an enerthenema, and says "the capillitial threads are some of them diffuse and bear spermatic globules"! Did he antic.i.p.ate _E. berkleyanum_? See the text under that species at p. 190, _supra_.

f. In a paper read December, 1920, before the _Mycological_ Division of Section G., _A. A. A. S._, the present writer discussed briefly the physical principles involved in some of the more striking peculiarities of the slime-moulds.

It is argued in that paper that the shaping of stipitate sporangia which is so surprising as relating to the ordinary behaviour of fluid ma.s.ses, as usually observed, is, in part at least, referable to certain well known properties of fluids generally. For this discussion those interested are referred to the article itself in the November number of _Mycologia_ (N. Y.).

Sufficient to say here that it is a fact, in many cases, that in stipitate fructification, so far as observed, the stipe is first to take form, and, as viewed by the writer, in many cases, as it rises, becomes more and more a most delicate but definite ectosarcate capillary tubule, by which ascends the spore-plasm of the point concerned, to such level as may meet the immediate conditions of pressure, of whatsoever source.

It will be interesting in this view to note the resultant shapes as presented in the sporangia of various genera. One may examine for ill.u.s.trations Figs. 1, 3, 4, 7, Pl. XX., with the thought in mind that the stipe in each case may have served as a capillary tubule to carry up the spore-plasm to the position in which the spores at length are found.

In some species of _Hemitrichia_, for instance, there are spores or spore-like cells found at maturity in the hollow stipe. In other cases the stipe contains refuse matter.

The capillary theory may not, probably does not, play part in every case. It would seem that a stemonitis, for example, must owe the rise of the spore-plasm to the play of different machinery. _Brefeldia_, p. 154 above, may offer suggestion.

g. On page two of the introductory section of this volume mention is made of the variety of colors shown in the vegetative phases of the organisms we study. This fact is patent to all observers; but the ident.i.ty of the plasmodium making the display must be ascertained by painstaking or prolonged and repeated observations. This for the reason that, as I am convinced, only in comparatively few cases is the color unchanged during the life-history of a given fructification. It may sometimes change from hour to hour as development proceeds. The color designated in the descriptive pages of this work is presumably, unless as otherwise set out, that immediately preceding that of the maturing fruit.

As suggestive, and as, it is hoped, contributory to better knowledge of this phase of our subject a list of species is here subjoined as presented by my colleague, Professor Morton E. Peck of Oregon, who has given unusual attention to this particular investigation.

SPECIES PLASMODIUM COLORS

_Physarum sinuosum_ light grey, nearly white, ivory white

_Physarum serpula_ greenish-yellow; yellow

_Physarum virescens_ pale greenish-yellow; yellow

_Physarum cinereum_ watery grey, becoming white; pallid

_Physarum didermoides_ watery grey, becoming white; blue-white

_Physarum notabile_ pure white

_Physarum globuliferum_ greenish-yellow; yellow

_Physarum leucopus_ light grey

_Physarum pulcherrimum_ dark red

_Physarum flavicomum_ greenish or brownish yellow

_Physarum viride_ clear yellow

_Physarum wingatense_ at first grey, then pure white

_Badhamia orbiculata_ pale yellow, pa.s.sing to white

_Physarella oblonga_ brilliant yellow

_Mucilago spongiosa_ watery grey, then white

_Didymium crustaceum_ white

_Didymium squamulosum_ pale grey, watery white

_Diderma floriforme_ grey tinged with yellow

_Stemonitis fusca_ white pa.s.sing through blue to black

_Stemonitis smithii_ green to yellow to reddish purple

_Comatricha longa_ white, cream-yellow, reddish purple to dusky

_Comatricha irregularis_ white

_Comatricha nigra_ white

_Comatricha typhoides_ bluish white

_Diachaea splendens_ pure white

_Enerthenema papillatum_ colorless or greenish

_Reticularia lycoperdon_ white

_Dictydiaethalium plumbeum_ colorless, pink, salmon, rose, orange, chocolate brown

_Lindbladia effusa_ brown, lead-colored

_Tubifera ferruginosa_ watery white, scarlet, brown, almost black

_Cribraria dictydioides_ clear dark green

_Cribraria tenella_ watery, dark plumbeous, bronze

_Cribraria cuprea_ red

_Arcyria nutans_ white

_Arcyria denudata_ watery white, then flesh-color

_Arcyria cinerea_ grey, then white

_Trichia varia_ colorless, then white

h. In a few instances references to ill.u.s.tration do not find place in connection with the descriptive matter. One phase of _Physarum albescens_ is figured on Pl. III.; _Mucilago_ will be found portrayed on Pl. VII.; _Physarum viride_ on Pl. VIII.

j. The group before us has research possibilities not a few. The question of their nutrition and its limits in respect of variety, is yet to be solved. From present indications all that can be said is to the effect that a pabulum similar in variety, no doubt meets the needs of many species. Whether in artificial culture a single base as gelatin or agar would suffice for all or several is yet to be discovered.

Whether a species brought from spore to maturity on artificial diet would conform in any reasonable way to our dim concept of its ident.i.ty is also, it would seem, a problem. The variation in the field would seem to make it doubtful.