746 



LECTURE XLII. 



the Phanerogams is essentially nothing different from the processes in the 

 germination of the large spores of those Cryptogams which possess two kinds of 

 spores. Hitherto it really appeared as if a deep and impassable gap existed 

 between the reproductive processes of the Cryptogams and Phanerogams ; but 

 Hofmeister showed thirty-one years ago that this gap does not really exist, that it is 

 filled up by those forms of Cryptogams which develope two kinds of spores ; or in 

 other words, certain forms of Phanerogams, particularly the Gymnosperms (Cycadeaä, 

 Coniferae) approximate in their seed-formation so closely to certain heterosporous 



Cryptogams, that we might now include these 

 plants equally justly with the Cryptogams as 

 with the Phanerogams. This discovery has cast 

 an entirely new light on the interdependence 

 of the whole vegetable kingdom. 



In the case of Marsilia, already shown in 

 Fig. 392 (p. 699), there arise from the petioles 

 of the foliage leaves stalked sporocarps approxi- 

 mately of the shape of a Bean. In the interior 

 of these a large number of delicate-walled spo- 

 rangia are formed, which at first are in so far 

 alike that in each of them a large number of 

 mother-cells are developed, which in their turn 

 divide each into four daughter -cells, as occurs 

 generally in the spore-formation of all Muscinese 

 and Vascular Cryptogams, and in the develop- 

 ment of the pollen of Phanerogams. From this 

 point onwards, however, a difference occurs. In 

 a number of the sporangia all the spores pro- 

 duced by division into four attain to complete 

 development; but they remain small and are 

 therefore called Microspores. In the other spo- 

 rangia of the same fruits, on the contrary, only 

 a single one of all the spore-cells already pro- 

 duced attains completion ; this one, however, 

 attains such vigour that it fills up the cavity of 

 the sporangium — it is the Macrospore. 



Lying in water the spore-fruit of the l\lar- 

 silia bursts, and by means of a very remarkable 

 mechanism the macro- and micro-sporangia 

 become expelled from the sporocarp (Fig. 430), whereupon the further development 

 of both kinds of spores begins at once. 



The contents of the microspores break up by successive bi-partitions into 

 sixteen or thirty-two small round cells, in each of which arises an antherozoid which 

 possesses the form of a cork-screw with many turns. As soon as the antherozoids 

 are completely developed, the external hard shell of the microspore opens, and an 

 inner thin membrane swells up as a vesicle, and eventually contains the antherozoids, 

 which then by deliquescence of the vesicle emerge free into the water, in which 



Pig. A^o.—Miii-suiasnlva/yix. A a sporo- 

 carp (nat. size) ; st upper part of its stalk B 

 a sporocarp burst in water and extruding the 

 gelatinous ring. C tile gelatinous ring is 

 ruptured and extended : sr chambers con- 

 taining sori ; scli coats of sporocarp. D one 

 of the chambers containing a sorus. from an 

 immature sporocarp. F. a similar chamber 

 from a ripe sporocarp : mi microsporangia ; 

 7na macrosporangia. 



