n^ 



LECTURE XLII. 



the ovule has become transformed into a thick pulpy mass which encloses a ' stone ' 

 like that of a plum, in which the endosperm is enclosed ; and matters are similar 

 in the Cycadese. In Cycas revohda the seeds attain the volume of a medium-sized apple. 

 In most of the Coniferse, however, the integument becomes transformed into a hard 

 seed-coat, and the seeds resemble those of other Phanerogams in other respects also. 

 A remark is still to be added regarding the pollen-grains of the Gymnosperms. 

 That these, from their developmental history and function and also from their 

 origin in receptacles which are obviously sporangia, are to be regarded as micro- 

 spores, has already been mentioned. A further similarity with microspores however 

 exists in the formation, in the interior of each pollen-grain, of a small cellular 

 body which calls to mind the sterile cells in the interior of the microspores of 

 Isbetes and Selaginelta. Fig. 439 shows the structure in question at j^, though it 

 is not equally well developed in all Gymnosperms. 

 Besides this structure, there still remains a large 

 mass in the pollen - grain or microspore, which 

 alone takes part in the development of the pollen- 

 tube, as may be seen in Fig. 439 B. This 

 portion of the pollen-grain, which contains the 

 fertilising substance, corresponds to the antheri- 

 dium of the microspore (as in the case of the 

 Rhizocarp Salvüiia), while the small cellular body j' 

 may be looked upon as the last remnant of a 

 reduced prothallium. 



With the Monocotyledons and Dicotyledons — 

 among which are found the most highly organised 

 plants in the vegetable kingdom, and which, apart 

 from the Coniferae, practically constitute what non- 

 botanical people are in the habit of thinking of 

 under the term ' plants,' — the Gymnosperms last con- 

 sidered agree as regards their reproduction in that 

 they give rise to ovules which are rendered fertile 

 by means of a pollen-tube, and then develope into a seed containing an embryo. 

 Hence all these plants may be contrasted, as Spermaphytes, with the Cryptogams 

 or Sporophytes. 



Nevertheless the fertilising apparatus of most Monocotyledons and Dicotyledons 

 appears to be strikingly different externally from that of the Gymnosperms. What 

 is commonly termed a flower is simply the fertilising apparatus of these plants 

 (which may therefore be contrasted as Flowering-plants in the narrower sense of 

 the word with the Gymnosperms), but here again it is of course to be borne in 

 mind that all such distinctions are only admissible when the typical forms in both 

 cases are contrasted with one another. It needs only a somewhat broader con- 

 ception of the idea Flower to justify the application of the term even to a Fir-cone 

 or even to the very unobvious fertilising apparatus of the Yew. Of course the 

 distinction between the flower of a Lily or of a Rose, and that of a Fir or Pine 

 or other Gymnosperm is very great, but between the two, even externally considered, 

 there are numerous stages of flower-development which show us that the difference 



FIG. 439.—^ a pollen-grain (microspore) of 

 Ceratozamia loiigi/olia, a Cycad. B emergence 

 of the pollen-tube ps from the ruptured outer 

 membrane (exline) of the pollen-grain. At j/ are 

 seen the sterile cells (Juranyi). 



