. Beginners' botany. Botany. 200 BEGINNERS' BOTANY dry weather the margins of the leaves roll inward, and the leaves fold closely against the stem, thus protecting the delicate assimi- lating tissue. The antheridia and archegonia of polytrichum are borne in groups at the ends of the branches on different plants (many mosses bear both organs on the same branch). They are sur- rounded by involucres of characteristic leaves termed perichcetia ox perichatal leaves. Multicellular hairs known as/ari7/;^jCJ« are scattered among the archegonia and antheridia. The involucres with the organs borne withi
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. Beginners' botany. Botany. 200 BEGINNERS' BOTANY dry weather the margins of the leaves roll inward, and the leaves fold closely against the stem, thus protecting the delicate assimi- lating tissue. The antheridia and archegonia of polytrichum are borne in groups at the ends of the branches on different plants (many mosses bear both organs on the same branch). They are sur- rounded by involucres of characteristic leaves termed perichcetia ox perichatal leaves. Multicellular hairs known as/ari7/;^jCJ« are scattered among the archegonia and antheridia. The involucres with the organs borne within them are called receptacles, or, less appropriately, " moss flowers." As in marchantia, the organs are very minute and must be highly magnified to be studied. The antheridia are borne in broad cup-like receptacles on the antheridial plants (Fig. 297). They are much like the antheridia of marchantia, but they stand free among the paraphyses and are not sunk in cavities. At maturity they burst and allow the sperm cells or spermatozoids to escape. In poly- trichum, when the receptacles have fulfilled their function, the stem con- FiG. 297. - SECTION THROUGH A tiuues to grow from the center of RECEPTACLE OF PoLVTRi- the cup (^, Fig. 295). The archc- CHUM COMMUNE showing gonia are bornc in Other rcceptacles paraphyses and antheridia. j-cr ^ 1 i mi i-i on different plants. They are like the archegonia of marchantia except that they stand erect on the end of the branch. The sporogonium which develops from the fertilized egg is shown in a, b, Fig. 295. It consists of a long, brown stalk bearing the spore-case at its summit. The base of the stalk is imbedded in the end of the moss stem by which it is nourished. The capsule is entirely inclosed by a hairy cap, the calyptra, b. The calyptra is really the remnant of the archegonium, which, for a time, increases in size to accommodate and protect the young growing capsule. It is finally torn loose and carried up on the spore-ca