2618 Journal of Applied Microscopy 



SUBKINGDOM, PTERIDOPHYTA. (HEThROSPOROUS.) 



LXVI. Marsilea quadrifolia L. European Marsilea. 



Class, Hydropterides. Order, Marsileales. Family, Marsileaceae. 



This water fern grows well in artificial ponds, in gardens and greenhouses. 

 The western Marsilea vestita H. & G. found in wet places and shallow ditches 

 on the great plains and prairies of the interior may also be used. 



Sporophytc. 



1. Sketch a branch of the creeping rhizome, showing the roots and the 

 leaves with slender upright petioles. 



2. Sketch a sporophyll with two sporocarps. 



3. Carefully cut otT part of the thick inner margin of some sporocarps and 

 place them in a glass of water. In a day or two a gelatinous ring will be 

 extruded on which are situated the sack-like sori in which microsporangia and 

 megasporangia are contained. Draw. 



4. Mount some of the microsporangia and megasporangia and draw each 

 under low power. The megasporangium contains a single megaspore ; the 

 microsporangium a considerable number of microspores. 



5. Under high power draw a single microspore and a megaspore, in correct 

 proportion. 



Gametophyte. 



6. In the meantime the spores will begin to develop the gametophytes. 

 These are very minute, and the spores in the water should be examined from 

 time to time in order to get the proper stages. The male gametophyte develops 

 entirely inside of the microspore wall and the female gametophyte merely pro- 

 trudes the neck of the archegonium from one end of the spore. Draw a male 

 gametophyte with a protrusion on the side of the spore wall for the escape of 

 the spermatozoids and a female gametophyte with archegonium projecting from 

 one end, showing a large number of spermatozoids in the gelatinous substance 

 extending from the neck of the archegonium. Why does the microspore always 

 give rise to a male plant, and the megaspore to a female ? 



7. If prepared slides are at hand, study and draw sections of mature male 

 and female gametophytes. The male gametophyte corresponds to the pollen 

 grain of seed plants, and the female gametophyte to the embryo-sac in the ovule. 

 Both gametophytes of Marsilea must be compared with the hermaphrodite game- 

 tophyte of Adiantum. Note especially the great reduction in size ; also that 

 after this there will be no more hermaphrodite gametophytes, hence no possi- 

 bility of self-fertilization. 



8. In a week or so the female plants in the glass of water will have embryo 

 sporophytes. Draw under low power and describe. 



9. Ecological note. — Examine a plant at night, or place a flower-pot with 

 a living plant in a dark chamber and note the manner in which the leaflets fold 

 up. How long does it take the leaflets to unfold after being placed in 

 sunlight ? 



