Fungi: Their Nature and Uses

by M. C. Cooke

It has already been remarked by us that the Saprolegnei are claimed by some authors as Algæ, whilst we are more disposed to regard them as closely allied to the Mucors, and as they exhibit in themselves strong evidence in support of the existence of sexual reproduction, we cannot forbear giving a summary of what has been observed by De Bary and others in this very interesting and singular group of plants, to which M. Cornu has recently dedicated an exhaustive monograph.[F]

In Saprolegnia monoica, and others, the female organs consist of oogonia—that is to say, of cells which are at first globose and rich in plastic matter, which most generally terminate short branches of the mycelium, and which are rarely seen in an interstitial position. The constitutive membrane of the adult oogonia is reabsorbed in a great many points, and is there pierced with rounded holes. At the same time the plasma is divided into a larger or smaller number of distinct portions, which are rounded into little spheres, and separate from the walls of the conceptacle in order to group themselves at the centre, where they float in a watery fluid. These gonospheres are then smooth and bare, with no membrane on their surface of the nature of cellulose.

Fig. 97.—Conjugation in Achlya racemosa. (Cornu.)

During the formation of the oogonia there arise from its pedicel or from neighbouring filaments slight cylindrical curved branches, sometimes turned round the support of the oogonia, and which all tend towards this organ. Their superior extremity is intimately applied to its wall, then ceases to be elongated, becomes slightly inflated, and is limited below by a partition; it is then an oblong cell, slightly curved, filled with protoplasm, and intimately applied to the oogonia—in fact, an antheridium or organ of the male sex. Each oogonium possesses one or several antheridia. Towards the time when the gonospheres are formed it may be observed that each antheridium sends to the interior of the oogonia one or several tubular processes, which have crossed its side wall, and which open at their extremity in order to discharge their contents. These, while they are flowing out, present some very agile corpuscles, and which, considering their resemblance to those in Vaucheria, to which the name of spermatozoids are applied, ought to be considered as the fecundating corpuscles. After the evacuation of the antheridia the gonospheres are found to be covered with cellulose; they then constitute so many oospores, with solid walls. De Bary considers that, bearing in mind analogous phenomena observed in Vaucheria, and the direct observations of Pringsheim,[G] the cellulose membrane on the surface of the gonospheres is only the consequence of a sexual fecundation.

In Achlya dioica the antheridium is cylindrical, the plasma which it encloses is divided into particles, which attain nearly the size of the zoospores of the same plant. These particles become globose cells, grouped in the centre of the antheridium. Afterwards the contents of these latter cells become divided into numerous bacillary spermatozoids, which first break the wall of their mother cell, and then issue from the antheridium. These rod-like corpuscles, which resemble the spermatozoids in Vaucheria, have their movements assisted by a long cilium. It is presumable that here, as in the Algæ, the spermatozoids introduce themselves into the cavity of the oogonium, and unite with the gonospheres.

Amongst obscure and doubtful bodies are those described by Pringsheim, which have their origin in thick filaments or tubes, similar to those which form the zoosporangia, and represent so many distinct little masses of plasma within an homogeneous parietal ganglion. The contour of these plastic masses is soon delineated in a more precise manner. We see in their interior some homogeneous granules, which are at first globose, then oval, and finally travel to the enlarged and ampullæform extremity of the generating tube. There they become rounded or oval cells covered with cellulose, and emit from their surface one or several cylindrical processes, which elongate towards the wall of the conceptacle, and pierce it, without, however, ever projecting very far beyond it. At the same time the lacunose protoplasm of each cell becomes divided into a number of corpuscles, which escape by the open extremity of the cylindrical neck. They resemble in their organization and agility the spermatozoids of Achlya dioica. They soon become motionless in water, and do not germinate. During the development of these organs, the protoplasm of the utricle which contains them offers at first completely normal characteristics, and disappears entirely by degrees as they increase. De Bary and Pringsheim believe that these organs constitute the antheridia of the species of Saprolegnia to which they belong.

The oospores of the Saprolegniæ, when arrived at maturity, possess a tolerably thick double integument, consisting of an epispore and an endospore. After a considerable time of repose they give rise to tubular or vesicular germs, which, without being much elongated, produce zoospores.[H]

De Bary has claimed for the oogonia in Cystopus and Peronospora a kind of fecundation which deserves mention here.[I] These same fruits, he says, which owe their origin to sexual organs, should bear the names of oogonia and antheridia, according to the terminology proposed by Pringsheim for analogous organs in the Algæ. The formation of the oogonia, or female organs, commences by the terminal or interstitial swelling of the tubes of the mycelium, which increase and take the form of large spherical or oboval cells, and which separate themselves by septa from the tube which carries them. Their membrane encloses granules of opaque protoplasm, mingled with numerous bulky granules of colourless fatty matter.