In the genera _Thamnidium_ and _Chætocladium_ the gradual diminution of the sporangia, and the reduction of the number of spores can be distinctly followed. In _Thamnidium_ the number of spores is often reduced to one, which is _free_ in the sporangium. In _Chætocladium_ however the sporangia are typically _one-spored_, the spore is always united with the sporangium, and the two become a single body, the so-called _conidium_, which is in reality a closed sporangium. How close is the connection between the sporangia and conidia of _Thamnidium_ and _Chætocladium_, is seen from the fact that, in the conidial stage of _Chætocladium_ the same whorl-form of branching appears as in the sporangial stages of _Thamnidium chætocladioides_, and also, that the conidia of _Ch. fresenianum_ throw off the former sporangium-wall (exosporium), while _Ch. jonesii_ germinates without shedding its exosporium. The Phycomycetes have doubtless sprung from Water-Algæ and inherit the sporangia from them. On this supposition, as the Phycomycetes assumed a terrestrial mode of life, the sporangia would become adapted to the distribution of the spores by means of the air, the sporangia would become small, contain dust-like spores, and would eventually become closed-sporangia, _i.e._ conidia. The conidia are a terrestrial method for the multiplication of Fungi. In the Hemiasci and the Ascomycetes the sporangia are still preserved, but in every instance they are adapted to terrestrial spore-distribution, their spores being set free on the destruction of the sporangium-wall (generally shot out) and distributed through the air. For further examples of spore-distribution see below, p. 91–93.