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Text Appearing After Image:Fig. 221. — Trichomanes cyrtotheca. Development of the sporangium, X22S. A,Longitudinal section of very young receptacle with the first sporangia isp); B-D,successive stages of development seen in longitudinal section; F, horizontal sectionof nearly ripe sporangium; r, the annulus. receptacle Is still very young the tissue of the leaf immediatelyabout it forms a ring-shaped ridge, which grows up in the formof a cup-shaped indusium, which either remains as a tube X THE HOMOSPOROUS LEPTOSPORANGIATJE 383 (Trichomancs) or is divided into two valves (Hymenophyl-him). Many species of the former genus, however, show anintermediate condition, with the margin of the indusium deeplytwo-lipped. The first sporangia arise at the top of the placenta (Fig.221), but the apex itself does not usually develop into a spo-rangium. After the first sporangia have formed, new onescontinue to develop. Near the base of the placenta a zone ofmeristem is formed, which constantly contributes to its growth,and t
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