. Our native ferns and their allies; with synoptical descriptions of the American Pteridophyta north of Mexico. Ferns; Pteridophyta. 22 OUR NATIVE FERNS AND THEIR oosphere, now called the oospore, increases in size, and finally develops into a true fern. 66. Pteridoid Phase.âAfter the oo- sphere has been fertilized it commences its growth by the ordinary processes of cell multiplication, and for a time remains with, in the walls of the archegonium, which continue to grow, until finally the interior growth breaks through the walls, differen- tiated into its first root and leaf. The you
. Our native ferns and their allies; with synoptical descriptions of the American Pteridophyta north of Mexico. Ferns; Pteridophyta. 22 OUR NATIVE FERNS AND THEIR oosphere, now called the oospore, increases in size, and finally develops into a true fern. 66. Pteridoid Phase.âAfter the oo- sphere has been fertilized it commences its growth by the ordinary processes of cell multiplication, and for a time remains with, in the walls of the archegonium, which continue to grow, until finally the interior growth breaks through the walls, differen- tiated into its first root and leaf. The young fern draws its nourishment from the pro- thallium for a time, but soon develops root-hairs, which, extending into the soil, maintain thereby an existence independent of the prothallium. The latter growth hav- FiG. it. ~ Adianium ing accomplished its work, withers away thi;Sm and';?ung £em (Fig- ^S). The first parts of the root, stem, protiiaUium- ^^ firat \tti- ^""^ f^ond are very small and comparatively h, root-hairs of prothai- simple in Structure, but those formed later Hum; w, «/', first and ... , , , second roots. (After are successively larger, and not only bear '^''^â ' a closer resemblance to the mature form of the species, but also develop increased complexity of struc- ture. " The fern continues to gain strength, not by subsequent increase of size of the embryonic structures, but by each succes- sive part attaining a more considerable size and development than the preceding ones, until at length a kind of stationary condition is arrived at, in which the newly formed organs are nearly similar to the preceding ; 67. The complete life-history of a fern illustrates a principle common among the lower forms of animal life known as "alter- nation of ; Instead of the direct production of a mature sexual plant, as among the higher forms of vegetation, there is the production of a sexual growth resembling a lower form of
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