|Notes: Plants Seedless|
Origins of Vascular Tissue.
resources are spatially separated.
soil = water and minerals but no light.
aerial = light but no water and minerals.
solved by regional specialization of plant areas.
problem = stand up straight, need support.
solution = lignin in cellular matrix; turgidity of cells helps small plants support themselves.
problem = tranport of materials between "organs:" water and minerals must
go up (to leaves), organic compounds must go down (to roots).
answer = a looping vascular system consisting of 2 tissues: xylem (dead tube cells carrying water and minerals up) and phloem (living cells moving amino acids, sugars, etc. down).
Later adaptations include the seed, pollen and diploid
The oldest known vascular plants were Cooksonia.
These are not true ferns. In diploid sporophyte form, they have a Y-branching system (dichotomous). They have no true roots and leaves but upright stems have protuberances that have not vascular tissue. To anchor themselves, Psilophytes have a rhizome - a horizontal stem covered with tiny hair-like structures called rhizoids.
These first evolved 340 million years ago. In 60 million years, Lycophyta split into the woody and nonwoody plants. Sporangia are created in leaf-like structures called sporophylls. Spores become underground gametophytes for 10 or more years with no photosynthesis only nurtured by fungi. The word "homosporous" means that there is 1 spore that can be either an egg or a sperm cell. "Heterosporous" indicates there is a megaspore (female) and a microspores (male). Lycopods can be either heterosporous or homosporous.
These date all the way back to the original vascular plants. Only one genus (Equisetum) has survived, located on stream banks. Dominant form is the sporophyte; the gametophyte is only a few millimeters long (but are independent photoautotrophs). It is homosporous.
These are the most diverse in the tropic and sat beside lycopods and horsetails. Megaphylls are the webbing of separate branches growing close to each other. Microphylls are tiny leaves originating with 1 strand of vascular tissue. Most have leaves called fronds. Fronds are compound (each leaf is divided into leaflets) and grows only at the coiled tip. May sprout horizontally, but tropical ferns tend to sprout their stems vertically and frow several feet. Often the sporangia are in clusters called sori on the underside of a frond with homosporous swimming gametes.
Next: "Plants: Gymnosperms."