ZOOLOGY AND BOTANY, MICUOSCOPY, ETC. 997 



beyond tlio appearance of the ai'cliesporo. Substiti;tionary growths may 

 take the form of (1) simple prolification ; (2) sporophoric budding ; or 

 (3) apospory. The seccT-i of these forms includes the well-known develop- 

 ment of bulbils on the fronds of some ferns. Aposj)ory includes all those 

 cases in which the substitutionary growth following sporal arrest results in 

 the formation of organs having the characteristics of the ooj)hore. This 

 occurs naturally in the cases of the ferns above-mentioned, and may be 

 induced artificially in mosses. In two of these there is a distinct transition 

 from the sporophore to the oophore without the intervention of spores, and 

 by a simple vegetative budding. In A. Filix-fem. var. clarissimum, the sub- 

 stitutionary growths which accompany the arrest of si^ore-formation are 

 restricted to the sporangium itself; while in P. angulare var. pulcherrimum, 

 the prothalloid growths may either proceed from the sorus, or may appear 

 at quite distinct spots, and even on fronds which bear no sori at all, and 

 comparable therefore in position to the common formation of sporophoric 

 buds on the fronds of ferns. 



The author concludes by comparing the aposporic phenomena in ferns 

 to the cases of arrest which occur either exceptionally or nominally in 

 mosses in CJiara and in Isoetes, and to the phenomenon of parthenogenesis 

 in flowering plants. 



Structure of Mucilaefe-cells of Blechnum occidentale and Osmunda 

 regalis.* — Messrs. W. Gardiner and Tokutaro Ito have examined the 

 cells which secrete the slimy mucilage in Blechnum occidentale, wherein 

 each hair of the terminal cell is glandular, and Osmunda regalia, vs^here all 

 the cells of the hair are usually secretory in function. They found that 

 the mucilage arises from the protoplasm only, and not from the cell-wall, 

 and that the whole process is distinctly intraprotoplasmic. The very words 

 used by Langley in the description of certain animal secretory cells may 

 be used of these ferns, for the cell-substance of the mature cells is com- 

 posed of a framework of protoplasm connected at the periphery with a thin 

 continuous layer of modified protoplasm (ectoplasm), while the meshes of 

 the framework inclose two chemical substances at least, a hyaline substance 

 in contact with the framework, and spherical granules imbedded in the 

 hyaline substance. In other words, the mucilage is secreted in the form 

 of drops, and each drop is further differentiated into a ground substance 

 (gum mucilage), in which are imbedded numerous spherical droplets 

 (gum). 



Secretion commences by the breaking down of a portion of the inner- 

 most layers of the protoj)lasm at a number of contiguous but isolated areas ; 

 the result is the formation of small but rapidly growing mucilage drops. 

 These last are at first watery and by no means well defined, biit they soon 

 become denser, and tannin is uniformly distributed throughout their struc- 

 ture. A delicate reticulation may now be observed in the drops, and this 

 finally gives way to the appearance of numerous minute and brightly 

 shining droj)lets, all separate and distinct. 



Usually plant-cells are incapable of the active and repeated secretion 

 which is seen in the animal secretory cells ; and those of Blechnum and 

 Osmunda die when they have formed their secretion ; but in other cases, 

 as e. g. the glands of Dionsea, it appears exceedingly probable that there 

 are periods of rest and of repeated secretion, as in animals. 



The secretion of the cells escapes by the rupturing of the cell-wall. In 

 Osmunda the whole system is perforated by fine holes, which in the 



* Ann. of Bot., i. (1887) pp. 27-54 (2 pis.), and Proc. Roy. Soc. Lond., xlii. (1887) 

 pp. 353-5. 



