Conjugation takes place in this way. Two threads of the mycelium which lie near each other put out each a short branch which is clavate in form. The ends of these branches meet, and in each a septum is formed which cuts off a portion of the protoplasm in the end from that of the rest of the mycelium. The meeting walls of the branches now dissolve and the protoplasm of each gamete fuses into one mass. A thick wall is now formed around this mass, and the outer layer becomes rough and brown. This is the _zygote_ or _zygospore_. The mycelium dies and it becomes free often with the suspensors, as the stalks of these sexual branches are called, still attached. This zygospore passes through a period of rest, when with the entrance of favorable conditions of growth it germinates, and usually produces directly a sporangium with gonidia. This completes the normal life cycle of the plant. =390. Gemmæ.=—Gemmæ, as they are sometimes called, are often formed on the mycelium. A short cell with a stout wall is formed on the side of a thread of the mycelium. In other cases large portions of the threads of the mycelium may separate into chains of cells. Both these kinds of cells are capable of growing and forming the mycelium again. They are sometimes called _chlamydospores_. [Illustration: Fig. 194. A mucor (Rhizopus nigricans); at left nearly mature sporangium with columella showing within; in the middle is ruptured sporangium with some of the gonidia clinging to the columella; at right two ruptured sporangia with everted columella.] =390=_a_. The Mucorineæ according to their manner of zygospore formation are of two kinds: 1st, the _homothallic_ (monœcious), in which all of the colonies of thalli developed from different spores are the same, and both gametes may be developed from the mycelium from a single spore, as in Sporodinia grandis, a mould common on old mushrooms; 2d, the _heterothallic_ (diœcious), in which certain plants are of a male nature and small in comparison with those of perhaps a female nature which are larger or more vigorous. When grown separately each of these two kinds of thalli, or colonies of mycelium, produce their own kind but only sporangia. If the two kinds are brought together, however, branches from one conjugate with branches from the other and zygospores are produced, as in Rhizopus nigricans, the common bread or fruit mould. This is one reason why we rarely find this fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the Mucorineæ, Proc. Am. Acad. Arts and Sci., =40=, 205-319, pl. 1-4, 1904.) Water Moulds (Saprolegnia). =391.= The water moulds are very interesting plants to study because they are so easy to obtain, and it is so easy to observe a type of gonidium here to which we have referred in our studies of the algæ, the motile gonidium, or zoogonidium. (See appendix for directions for cultivating this mould.)