410 



BOTANY 



(Fig. 



the unruptured microsporangium, -each germinating microspore puts 

 out a short tubular male prothallium, which pierces the sporangial 

 wall. In this process the microspore first divides into three cells 

 344, A, I-III) ; the lowest (/) then cuts off a small lenticular- 

 shaped cell (B, p), which may be re- 

 garded as the rudiment of an unde- 

 veloped root-hair cut off from the larger 

 cell a. The latter (a) thereupon elon- 

 gates and pushes the other two cells (II, 

 III) out of the microsporangium. These 

 two cells each give rise, by further 

 division, to two sterile cells and two 

 spermatogenous cells, representing two 

 antheridia with their respective sterile 

 wall-cells. Each antheridium produces 

 four spermatozoids, which are set free 

 by the rupture of the cell walls. 

 Although the whole male prothallium 

 is thus greatly reduced, it nevertheless 

 exhibits in its structure a pronounced 

 resemblance to the prothallia of the 

 Filices. 



The MACROSPORANGIA are larger 

 than the microsporangia, but their walls 

 consist similarly of one cell-layer (Fig. 

 343, D). Each macrosporangium pro- 

 duces only a single large macrospore, 

 which develops at the expense of the 

 numerous spores originally formed. The 

 The ceils s lSl and s 2 s 2 represent two macrospore j s densely filled with large 



antheridia; the cells b, c, d } e- their , ., . / -r. ti \*i 



wail-ceils. (After belajeff.) angular proteid grams (D, E,a), oil 



globules, and starch grains ; at its apex 

 the protoplasm is denser and contains the nucleus (E, n) ; the mem- 

 brane of the spore is covered by a dense brown exinium (E, e), which 

 in turn is enclosed in a thick frothy envelope, the perinium, investing 

 the whole spore and corresponding to the interstitial substance of the 

 microspores, and also formed from the dissolution of the tapetal cells. 

 The macrospore remains within the sporangium, which is eventually 

 set free from the mother plant. On the germination of the macro- 

 spore, a small-celled female prothallium is formed by the division of 

 the denser protoplasm at the apex, while the large underlying cell 

 does not take part in the division, but from its reserve material pro- 

 vides the developing prothallium with nourishment. The spore wall 

 splits into three valves, the sporangia are ruptured, and the green 

 prothallium protrudes as a small saddle-shaped body. On it three 

 archegonia are produced, but only the fertilised egg-cell of one of 



Fig. 344. — Salvinia nctfans. Development 

 of the male prothallium. A, Division 

 of the microspore into three cells 

 I-III ( x 860) ; B, lateral view ; C, ven- 

 tral view of mature prothallium (x 

 640). Cell I has divided into the pro- 

 thallium cells a and p ; cell II, into the 

 sterile cells &, c, and the two cells si, 

 each of which has formed two sperma- 

 tozoid mother-cells ; cell III, into the 

 sterile cells d, e. and the two cells so- 



